Stabilize garbage collection tests

[psalin]

The client_stream_garbage_collect_streams test occasionally fails because sometimes the check for collected streams is run before the streams have been finished. To stabilize the test, allow some retries to ensure the stream has enough time to be collected.

[codecov[bot]]

Codecov Report

Base: 39.02% // Head: 39.02% // No change to project coverage :thumbsup:

Coverage data is based on head (549b907) compared to base (8cad52b). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #92 +/- ## ======================================= Coverage 39.02% 39.02% ======================================= Files 28 28 Lines 2091 2091 ======================================= Hits 816 816 Misses 1275 1275 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tristan+Sloughter). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Tristan+Sloughter)

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[tsloughter]

Did you forget to include some part of this patch? I only see a sleep added and not retries?

[psalin]

Well it only needs a couple of ms so 100ms sleep is more than enough for it to not fail. With so short times the original retry solution was overkill and I removed it.