fix: Adjust filename validation messages

[susnux]

• Resolves: Improve Error Message Clarity When Moving or Copying Files to Invalid Folders #47096

Summary

Adjust error messages to be consistent with clients.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)

[susnux]

/backport to stable30

[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/47546/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 81c6c24c

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/47546/stable30

Error: Failed to clone repository: Failed to checkout branches: error: Your local changes to the following files would be overwritten by checkout:
dist/3794-3794.js.map.license
dist/4546-4546.js.map.license
dist/4696-4696.js.map.license
dist/5643-5643.js.map.license
dist/583-583.js.map.license
dist/9972-9972.js.map.license
Please commit your changes or stash them before you switch branches.
Aborting

---

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

[AndyScherzinger]

Since I am AFK, could you please do a manual backport @susnux? Thanks 🙏

[skjnldsv]

/backport to stable30