Retry test failures on Unity

[jonsimantov]

Description

Provide details of the change, and generalize the change in the PR title above.

It will retry all build errors that match timeout/network error regexes, but not any compiler errors or other issues. (If there are other instances in which the builds sometimes fail transiently, we can add that.)

Not sure under what conditions to actually trigger the test retry, so it does it unconditionally.

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Testing

Describe how you've tested these changes.

Tested manually with the "scheduled_trigger" check in integration_tests.yaml commented out, and failure forced.

This run: https://github.com/firebase/firebase-unity-sdk/actions/runs/9087398748

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Type of Change

Place an x the applicable box:

• [ ] Bug fix. Add the issue # below if applicable.
• [ ] New feature. A non-breaking change which adds functionality.
• [ ] Other, such as a build process or documentation change.

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