chore(i18n): Fix grammar in error message for file sharing

[rakekniven]

Reported at Transifex

[lukasdotcom]

Thanks

[rakekniven]

Please backport it to all branches synced to Tx.

[rakekniven]

/backport to stable33

[backportbot]

The backport to stable33 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable33
git pull origin stable33

# Create the new backport branch
git checkout -b backport/400/stable33

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick ecfc1806

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/400/stable33

Error: Failed to clone repository: Failed to create working tree: Preparing worktree (new branch 'backport/400/stable33')
fatal: not a valid object name: 'origin/stable33'

---

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

[rakekniven]

/backport to stable32