Issue:
ci: run tests on PRs with `S-awaiting-merge` label

## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates

## Description
<!-- Describe your changes in detail -->
This PR updates the CI workflow to run tests when PRs are labeled `S-awaiting-merge`. This could either be when the PR is opened, reopened, marked ready for review (from a draft PR), assigned a label, or synchronized with the base branch.

## Motivation and Context
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We often have people opening WIP PRs which unnecessarily use CI resources with no fruitful results. This change is a hopeful attempt to prevent that.

## How did you test it?
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Did you write an integration/unit/API test to verify the code changes?
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Haven't tested it, "I hope it works" (TM). :crossed_fingers:

## Checklist
<!-- Put an `x` in the boxes that apply -->

- [ ] I formatted the code `cargo +nightly fmt`
- [ ] I addressed lints thrown by `cargo clippy`
- [x] I reviewed submitted code
- [ ] I added unit tests for my changes where possible
- [ ] I added a [CHANGELOG](/CHANGELOG.md) entry if applicable

Resolution:
<think>
PR Context:
- Title: ci: allow tests to run on push to `main` branch
- Merged: 2022-12-19T08:09:11Z
- Files changed: 2 files
- Commits: 1 commits

Implementation approach:
## Type of Change
<!-- Put an `x` in the boxes that apply -->

- [ ] Bugfix
- [ ] New feature
- [ ] Enhancement
- [ ] Refactoring
- [ ] Dependency updates

## Description
<!-- Describe your changes in detail -->
This PR fixes a minor mistake in #166 where I forgot to allow tests on the `main` branch.

## Motivation and Context
<!--
Why is this change required? What problem does it solve?
If it fixes an open issue, please link to the issue here.

If you don't have an issue, we'd
</think>

To implement this, you'll need to modify:


(No detailed commit information available)