Mac framework_tests_libraries is 3.03% flaky

[flutterflakybot]

The post-submit test builder Mac framework_tests_libraries had a flaky ratio 3.03% for the past 15 days, which is above our 2.00% threshold.

One recent flaky example for a same commit: https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1344
Commit: flutter@7a73915
Failed build:
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1344
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1336
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1325
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1318
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1315
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1312
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1311
Succeeded build (3 most recent):
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1515
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1514
https://ci.chromium.org/ui/p/flutter/builders/prod/Mac%20framework_tests_libraries/1513

Please follow https://github.com/flutter/flutter/wiki/Reducing-Test-Flakiness#fixing-flaky-tests to fix the flakiness and enable the test back after validating the fix (internal dashboard to validate: go/flutter_test_flakiness).