Repository: flutter
Issue: flutter upgrade fails using Cygwin git: "fatal: Needed a single revision"
Labels: c: crash,tool,platform-windows,P3,team-tool,triaged-tool

## Steps to Reproduce

1. Download and unzip into a directory, e.g. D:\personal-dev\flutter
2. Set PATH env var to include flutter\bin, e.g. D:\personal-dev\flutter\bin
3. run flutter channel stable
```bash
D:\personal-dev\flutter>flutter channel stable
Downloading package sky_engine...                                   0.5s
Downloading flutter_patched_sdk tools...                            0.5s
Downloading flutter_patched_sdk_product tools...                    0.4s
Downloading windows-x64 tools...                                    0.9s
Downloading windows-x64/font-subset tools...                        0.1s
Switching to flutter channel 'stable'...
git: Already on 'stable'
git: Your branch is up to date with 'origin/stable'.
Successfully switched to flutter channel 'stable'.
To ensure that you're on the latest build from this channel, run 'flutter upgrade'
```
4. run flutter upgrade
```bash
D:\personal-dev\flutter>flutter upgrade -v
[ +123 ms] executing: [D:\personal-dev\flutter/] git -c log.showSignature=false log -n 1 --pretty=format:%H
[ +125 ms] Exit code 0 from: git -c log.showSignature=false log -n 1 --pretty=format:%H
[   +1 ms] 78910062997c3a836feee883712c241a5fd22983
[   +1 ms] executing: [D:\personal-dev\flutter/] git tag --points-at HEAD
[ +107 ms] Exit code 0 from: git tag --points-at HEAD
[   +1 ms] 1.22.5
[  +20 ms] executing: [D:\personal-dev\flutter/] git rev-parse --abbrev-ref HEAD
[  +91 ms] Exit code 0 from: git rev-parse --abbrev-ref HEAD
[        ] stable
[  +84 ms] executing: [D:\personal-dev\flutter/] git tag --points-at HEAD
[ +102 ms] Exit code 0 from: git tag --points-at HEAD
[        ] 1.22.5
[   +3 ms] executing: [D:\personal-dev\flutter/] git fetch --tags
[+1604 ms] executing: [D:\personal-dev\flutter/] git rev-parse --verify @{u}
[  +87 ms] fatal: Needed a single revision
[  +11 ms] "flutter upgrade" took 1,831ms.
[   +5 ms] ProcessException: Process exited abnormally:
           fatal: Needed a single revision
             Command: git rev-parse --verify @{u}
[   +3 ms]
           #0      throwToolExit (package:flutter_tools/src/base/common.dart:14:3)
           #1      UpgradeCommandRunner.fetchRemoteRevision (package:flutter_tools/src/commands/upgrade.dart:237:9)
           <asynchronous suspension>
           #2      UpgradeCommandRunner.runCommandFirstHalf (package:flutter_tools/src/commands/upgrade.dart:103:43)
           #3      UpgradeCommandRunner.runCommand (package:flutter_tools/src/commands/upgrade.dart:85:13)
           #4      UpgradeCommand.runCommand (package:flutter_tools/src/commands/upgrade.dart:60:27)
           #5      FlutterCommand.verifyThenRunCommand (package:flutter_tools/src/runner/flutter_command.dart:977:18)
           #6      _rootRunUnary (dart:async/zone.dart:1198:47)
           #7      _CustomZone.runUnary (dart:async/zone.dart:1100:19)
           #8      _FutureListener.handleValue (dart:async/future_impl.dart:143:18)
           #9      Future._propagateToListeners.handleValueCallback (dart:async/future_impl.dart:696:45)
           #10     Future._propagateToListeners (dart:async/future_impl.dart:725:32)
           #11     Future._completeWithValue (dart:async/future_impl.dart:529:5)
           #12     Future._asyncCompleteWithValue.<anonymous closure> (dart:async/future_impl.dart:567:7)
           #13     _rootRun (dart:async/zone.dart:1190:13)
           #14     _CustomZone.run (dart:async/zone.dart:1093:19)
           #15     _CustomZone.runGuarded (dart:async/zone.dart:997:7)
           #16     _CustomZone.bindCallbackGuarded.<anonymous closure> (dart:async/zone.dart:1037:23)
           #17     _microtaskLoop (dart:async/schedule_microtask.dart:41:21)
           #18     _startMicrotaskLoop (dart:async/schedule_microtask.dart:50:5)
           #19     _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:118:13)
           #20     _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:169:5)


[ +185 ms] ensureAnalyticsSent: 182ms
[   +2 ms] Running shutdown hooks
[        ] Shutdown hooks complete
[        ] exiting with code 1
```
This seems to be a problem related to the stable git repo?

<details>


<summary>Logs</summary>

```bash
D:\personal-dev\flutter>flutter doctor -v
[✓] Flutter (Channel @u, 1.22.5, on Microsoft Windows [Version 10.0.19582.1001], locale en-CA)
    • Flutter version 1.22.5 at D:\personal-dev\flutter
    • Framework revision 7891006299 (5 weeks ago), 2020-12-10 11:54:40 -0800
    • Engine revision ae90085a84
    • Dart version 2.10.4

[✓] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[!] Android Studio (version 4.1.0)
    • Android Studio at C:\Program Files\Android\Android Studio
    ✗ Flutter plugin not installed; this adds Flutter specific functionality.
    ✗ Dart plugin not installed; this adds Dart specific functionality.
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[✓] VS Code (version 1.52.1)
    • VS Code at C:\Users\bdillman\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.18.0

[✓] Connected device (2 available)
    • Web Server (web) • web-server • web-javascript • Flutter Tools
    • Chrome (web)     • chrome     • web-javascript • Google Chrome 87.0.4280.141

! Doctor found issues in 1 category.
```

</details>