chore: Remove Code Coverage requirements

[lqiu96]

91% code coverage is quite high. We'll rely on maintainers and developers for best effort of coverage on implementations instead of an arbitrary metric.

This also removes issues from local development:

[WARNING] Rule violated for bundle google-auth-library-oauth2-http: lines covered ratio is 0.881, but expected minimum is 0.910
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Summary for Google Auth Library for Java 1.43.1-SNAPSHOT:
[INFO]
[INFO] Google Auth Library for Java ....................... SUCCESS [  1.582 s]
[INFO] Google Auth Library for Java - Credentials ......... SUCCESS [  1.814 s]
[INFO] Google Auth Library for Java - OAuth2 HTTP ......... FAILURE [01:05 min]
[INFO] Google Auth Library for Java - Google App Engine ... SKIPPED
[INFO] Google Auth Library for Java BOM ................... SUCCESS [  0.082 s]
[INFO] Google Auth Library for Java - Cab Token Generator . SKIPPED
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  01:09 min (Wall Clock)
[INFO] Finished at: 2026-03-19T17:12:36-04:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.jacoco:jacoco-maven-plugin:0.8.12:check (jacoco-check) on project google-auth-library-oauth2-http: Coverage checks have not been met. See log for details. -> [Help 1]
[ERROR]
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/MojoExecutionException
[ERROR]
[ERROR] After correcting the problems, you can resume the build with the command
[ERROR]   mvn <args> -rf :google-auth-library-oauth2-http

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud