temporarily use mac-os version 11.0 to avoid emulator timeout.

[epicadk]

IMPORTANT: All PRs must be linked to an issue (except for extremely trivial and straightforward changes).

Fixes # trivial

Description
Clear and concise code change description.

use mac-os version 11.0 to avoid emulator timeout.

see
current version
https://github.com/google/android-fhir/runs/2888614202

after using mac-os version 11.0
https://github.com/google/android-fhir/runs/2891412388

Alternative(s) considered
Have you considered any alternatives? And if so, why have you chosen the approach in this PR?

see ReactiveCircus/android-emulator-runner#160

Type
Choose one: Other

Screenshots (if applicable)

Checklist

• I have read and acknowledged the Code of conduct
• I have read How to Contribute
• I have read the Developer's guide
• I have signed the Google Individual CLA, or I am covered by my company's Corporate CLA
• I have discussed my proposed solution with code owners in the linked issue(s) and we have agreed upon the general approach
• I have run ./gradlew spotlessApply and ./gradlew spotlessCheck to check my code follows the style guide of this project
• I have run ./gradlew check and ./gradlew connectedCheck to test my changes locally
• I have built and run the reference app(s) to verify my change fixes the issue and/or does not break the reference app(s)

[jingtang10]

thanks @epicadk! 🤞