Add recent Android API levels to instrumentation test matrix

Add API levels 28, 29, 31, 33, and 34 (Android 9-14) to the CI
emulator matrix. API 29 was previously marked flaky but is worth
retrying with current tooling. All use x86_64 + google_apis + stable
channel, consistent with the existing modern emulator configuration.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>