`AuthService test` unit tests fail more frequently than other test suites in CI

[MMilosz]

Describe the bug

It seems the AuthService test suite fails more often than other test suites during the GitHub Actions build step, and these failures do not happen locally.

Interestingly, re-triggering the build step makes the tests pass, suggesting a possible race condition, cache problems, or other timing-sensitive issue within the AuthService (or its test setup)

To Reproduce

1. Go to the GitHub Actions Build workflow page.
2. Look for recent non-CRIS, non-Dependabot triggered builds (status doesn't matter).
3. (Optional) In the top right of a build summary, check the 'Attempts' dropdown and select the latest failed build.
4. Scroll down to the 'Annotations' section for the 'tests (22.x)' or 'tests (20.x)' job. In most cases, the failure comes from the AuthService test.

Examples

• ✖ should return token object when it is valid: https://github.com/DSpace/dspace-angular/actions/runs/30265995039/job/89976681695#step:13:9766
• ✖ should return a token object: https://github.com/DSpace/dspace-angular/actions/runs/29429629870/job/87400960802#step:13:10113
• AuthService test should return false when token is not expired FAILED Error: Expected null to be false.: https://github.com/DSpace/dspace-angular/actions/runs/30375025302/job/90328359170?pr=5995#step:13:8565

Expected behavior

The AuthService test suite should pass consistently like other test suites

Related work

• fix(auth): ensure isTokenExpired returns strict boolean #6002 #6003

[MMilosz]

I'm currently working on 1 (perhaps 2) PRs that may address this issue. I'll link them here shortly once I've verified if they could resolve the issue