fix(tests): use delta tolerance for lock ETA assertions to prevent flaky test failures

[juliusknorr]

This PR fixes a flaky test failure in LockFeatureTest::testExtendLock where timing precision issues caused assertions to fail by 1 second (expecting 900 but getting 901).

[juliusknorr]

/backport to stable32

[juliusknorr]

/backport to stable31

[juliusknorr]

/backport to stable30

[juliusknorr]

/backport to stable29

[backportbot]

The backport to stable30 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable30
git pull origin stable30

# Create the new backport branch
git checkout -b backport/904/stable30

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 0662d05a

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/904/stable30

Error: Failed to check for changes with origin/stable30: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.

[backportbot]

The backport to stable29 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable29
git pull origin stable29

# Create the new backport branch
git checkout -b backport/904/stable29

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 0662d05a

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/904/stable29

Error: Failed to check for changes with origin/stable29: No changes found in backport branch

---

Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.