Flaky TestRegisterUserPreAuthAfterUnlock

[adombeck]

https://github.com/ubuntu/authd/actions/runs/16645594204/job/47105379807?pr=1027#step:13:60

📦 github.com/ubuntu/authd/internal/users
❌ TestRegisterUserPreAuthAfterUnlock (16.01s)
  2025/07/31 09:47:28 DEBUG TestOverrideExternallyLocked: Local entries external lock released!
      manager_test.go:1147: 
          	Error Trace:	/home/runner/work/authd/authd/internal/users/locking/testutils.go:167
          	            				/home/runner/work/authd/authd/internal/users/manager_test.go:1147
          	Error:      	Received unexpected error:
          	            	failed waiting for 16s: failed to lock the system's user database: timeout
          	Test:       	TestRegisterUserPreAuthAfterUnlock
          	Messages:   	Locking should be allowed
  2025/07/31 09:47:44 DEBUG TestOverrideExternallyLocked: Local entries unlocked!