fix: Use lock owner display name on error response

[juliusknorr]

Fix #250

[susnux]

@juliushaertl do we backport?

[juliusknorr]

/backport to stable28

[juliusknorr]

/backport to stable27

[backportbot]

The backport to stable28 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable28
git pull origin stable28

# Create the new backport branch
git checkout -b backport/251/stable28

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 5acd287d

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/251/stable28

Error: 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 stable27 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable27
git pull origin stable27

# Create the new backport branch
git checkout -b backport/251/stable27

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 5acd287d

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/251/stable27

Error: No changes found in backport branch

---

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

[susnux]

/backport to stable28

[backportbot]

The backport to stable28 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable28
git pull origin stable28

# Create the new backport branch
git checkout -b backport/251/stable28

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 5acd287d

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/251/stable28

Error: No changes found in backport branch

---

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

[juliusknorr]

Needs a backport of #231 first

[juliusknorr]

/backport to stable28

[juliusknorr]

/backport to stable27