Avoid catching FlutterError in TextPainter tests

[tgucio]

This PR swaps catching FlutterError with expect in TextPainter tests (missed in #127307).

test-exempt: no functional change (only test code changed)

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• All existing and new tests are passing.

[auto-submit]

auto label is removed for flutter/flutter, pr: 127604, due to This PR has not met approval requirements for merging. You are a member of flutter-hackers and need 1 more review(s) in order to merge this PR.

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