Minor grammatical fix to runner deletion message (go-gitea#7479)

WIP until someone else tells me whether the whole message should be changed or whether `s/mark/marked/` is enough.
I am honestly not sure what "It may break building workflow." means in this context either but it doesn't sound correct to me.

## Checklist
*snipped* - this is really minor, please let me know if there's a better checklist to use for changes like this

### Release notes

- [x] I do not want this change to show in the release notes.  [Change is too minor]

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7479
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: voltagex <git@voltagex.org>
Co-committed-by: voltagex <git@voltagex.org>

Author: voltagex

options/locale/locale_en-US.ini

@@ -3871,7 +3871,7 @@ runners.delete_runner = Delete this runner
 runners.delete_runner_success = Runner deleted successfully
 runners.delete_runner_failed = Failed to delete runner
 runners.delete_runner_header = Confirm to delete this runner
-runners.delete_runner_notice = If a task is running on this runner, it will be terminated and mark as failed. It may break building workflow.
+runners.delete_runner_notice = If a task is running on this runner, it will be terminated and marked as failed. It may break building workflow.
 runners.none = No runners available
 runners.status.unspecified = Unknown
 runners.status.idle = Idle