Fix and reduce coverage targets

[jtuttle]

What does this PR do?

Coverage targets are thresholds with the format "healthy, unhealthy, unstable" so each threshold moving from left to right should be equal to or less than the previous one.

I'm also reducing the line coverage threshold because it's currently failing on a commit that only made changes to the CHANGELOG, so cobertura may be analyzing more files than it should be.

Change log

• [ ] The CHANGELOG has been updated, or
• [x] This PR does not include user-facing changes and doesn't require a CHANGELOG update

Test coverage

• [ ] This PR includes new unit and integration tests to go with the code changes, or
• [x] The changes in this PR do not require tests

Documentation

• [ ] Docs (e.g. READMEs) were updated in this PR, and/or there is a follow-on issue to update docs, or
• [x] This PR does not require updating any documentation

[jtuttle]

Closing in favor of a proper solution that adds test coverage for the new JWT authenticator.