fix: proper locking of memory store

[mitar]

Related Issue or Design Document

We use memory store for tests and we noticed race conditions failing those tests occasionally. It looks like locking was not correct in memory store.

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
  If this pull request addresses a security vulnerability,
  I confirm that I got approval (please contact [email protected]) from the maintainers to push the changes.
• I have added tests that prove my fix is effective or that my feature works.
• I have added the necessary documentation within the code base (if appropriate).

[mitar]

OIDC Conformity Tests have timed out. I do not think this is because of this PR.

[aeneasr]

Hm, CI timeout usually means some test(s) failed. But yeah, strange why they fail. Mabye re-running helps

[mitar]

@aeneasr It does not seem I have permissions to do a re-run?

[mitar]

@alnr Thanks for re-run.

I think this is a bug in current testing suite, also unrelated #854 is failing with exactly the same "Test was INTERRUPTED" errors while testing, and then test harness tries to repeat the test, again and again. And this is why the whole run then timeouts.

So I think somebody should try to run CI on the master branch and fix it there first.