Add error checking to flaky test bot platform parser (#86632)
If an invalid platform is specified when disabling a test with flaky test bot, the CI crashes, skipping all tests that come after it.
This turns it into a console message instead. Not erroring out here since it'll affect random PRs. Actual error message should go into the bot that parses the original issue so that it can respond on that issue directly
Pull Request resolved: https://github.com/pytorch/pytorch/pull/86632
Approved by: https://github.com/huydhn
