Repository: promptfoo/promptfoo
Issue: Bug: Vars glob expansion on referenced test file broken in 0.117.9
Root cause: Algorithmic Error

**Describe the bug**

Test files are supposed to be able to do glob expansion on vars to create multiple tests (one for each file).
When upgrading from 0.117.8 to 0.117.9, the vars expansion breaks (no other changes were introduced except for updating promptfoo version).
Instead of creating a new TestCase for each file in the glob, it erroneously creates a single TestCase with an array of stringified objects. 

*0.177.8 Behavior (Correct)*
<img width="1507" height="368" alt="Image" src="https://github.com/user-attachments/assets/3aa3afb9-053e-4276-b64c-393421ed05a2" />

*0.177.9 Behavior (Incorrect)*
<img width="1515" height="532" alt="Image" src="https://github.com/user-attachments/assets/3ec26fda-9084-4ed0-b9f5-1108a00d53bc" />


**To Reproduce**

1. Create project with the following files:

`package.json`
```
{
  "name": "promptfoo-glob-repro",
  "private": true,
  "scripts": {
    "eval": "promptfoo eval -c promptfooconfig.yaml -o out.json --no-cache"
  },
  "devDependencies": {
    "promptfoo": "0.117.8"
  }
}
```

`promptfooconfig.yaml`
```
# Note: This references another test file (required to repro)
tests: file://myTests.yaml

prompts:
  - 'Repeat this phrase back to me: {{text}}'

sharing: false

providers:
  - id: echo
```

`myTests.yaml`
```
- vars:
    text: file://./resources/tests/*.json
  assert:
    - type: contains
      value: hello
```

`resources/tests/one.yaml`
```
{ "text": "hello one" }
```

`resources/tests/two.yaml`
```
{ "text": "hello two" }
```

2. Validate that everything works in 0.117.8

```
npm i
npm run eval
# should have 2 successes
```

3. Change package.json to use 0.117.9 and validate broken behavior

```
# after changing version in package.json to 0.117.9
npm i
npm run eval
# should have single test failure with [object Object],[object Object]
```

**Expected behavior**
There should be two successful test cases.
See screenshots above.

**System information:**

Here is promptfoo debug when using the broken 0.117.9
```
$ npx promptfoo debug

===============================================================================================================================================================================================================
⚠️ The current version of promptfoo 0.117.9 is lower than the latest available version 0.118.7.

Please run npx promptfoo@latest or npm install -g promptfoo@latest to update.
===============================================================================================================================================================================================================

===============================================================================================================================================================================================================
Promptfoo Debug Information
===============================================================================================================================================================================================================
{
  "version": "0.117.9",
  "platform": {
    "os": "darwin",
    "release": "24.1.0",
    "arch": "arm64",
    "nodeVersion": "v20.17.0"
  },
  "env": {},
  "configInfo": {
    "defaultConfigPath": "/Users/matthertogs/Sandbox/promptfoo-glob-repro/promptfooconfig.yaml",
    "configExists": true,
    "configContent": {
      "config": {
        "tags": {},
        "prompts": [
          "Repeat this phrase back to me: {{text}}"
        ],
        "providers": [
          {
            "id": "echo"
          }
        ],
        "tests": [
          {
            "vars": {
              "text": [
                {
                  "text": "hello two"
                },
                {
                  "text": "hello one"
                }
              ]
            },
            "assert": [
              {
                "type": "contains",
                "value": "hello"
              }
            ]
          }
        ],
        "scenarios": [],
        "env": {},
        "sharing": false,
        "outputPath": [],
        "extensions": [],
        "metadata": {}
      },
      "testSuite": {
        "tags": {},
        "prompts": [
          {
            "raw": "Repeat this phrase back to me: {{text}}",
            "label": "Repeat this phrase back to me: {{text}}"
          }
        ],
        "providers": [
          {
            "options": {
              "id": "echo",
              "config": {
                "basePath": "/Users/matthertogs/Sandbox/promptfoo-glob-repro"
              },
              "env": {}
            },
            "label": "",
            "config": {
              "basePath": "/Users/matthertogs/Sandbox/promptfoo-glob-repro"
            }
          }
        ],
        "providerPromptMap": {
          "echo": [
            "Repeat this phrase back to me: {{text}}"
          ]
        },
        "tests": [
          {
            "vars": {
              "text": [
                {
                  "text": "hello two"
                },
                {
                  "text": "hello one"
                }
              ]
            },
            "assert": [
              {
                "type": "contains",
                "value": "hello"
              }
            ]
          }
        ],
        "scenarios": [],
        "defaultTest": {
          "metadata": {},
          "options": {}
        },
        "nunjucksFilters": {},
        "extensions": []
      },
      "basePath": "/Users/matthertogs/Sandbox/promptfoo-glob-repro"
    }
  }
}
```

**Additional context**

This only reproduces when the promptfooconfig.yaml references another test file. If you do test var glob expansion directly in promptfooconfig.yaml, it still works.

Additionally, this problem still recurs in the latest version of promptfoo (0.118.7)