Prevent simultaneous editing of comments and issues (#31053)

fixes #22907 

Tested:
- [x] issue content edit
- [x] issue content change tasklist
- [x] pull request content edit
- [x] pull request change tasklist

![issue-content-edit](https://github.com/go-gitea/gitea/assets/29250154/a0828889-fb96-4bc4-8600-da92e3205812)

options/locale/locale_en-US.ini

@@ -1443,6 +1443,7 @@ issues.new.clear_assignees = Clear assignees
 issues.new.no_assignees = No Assignees
 issues.new.no_reviewers = No reviewers
 issues.new.blocked_user = Cannot create issue because you are blocked by the repository owner.
+issues.edit.already_changed = Unable to save changes to the issue. It appears the content has already been changed by another user. Please refresh the page and try editing again to avoid overwriting their changes
 issues.edit.blocked_user = Cannot edit content because you are blocked by the poster or repository owner.
 issues.choose.get_started = Get Started
 issues.choose.open_external_link = Open
@@ -1758,6 +1759,7 @@ compare.compare_head = compare
 pulls.desc = Enable pull requests and code reviews.
 pulls.new = New Pull Request
 pulls.new.blocked_user = Cannot create pull request because you are blocked by the repository owner.
+pulls.edit.already_changed = Unable to save changes to the pull request. It appears the content has already been changed by another user. Please refresh the page and try editing again to avoid overwriting their changes
 pulls.view = View Pull Request
 pulls.compare_changes = New Pull Request
 pulls.allow_edits_from_maintainers = Allow edits from maintainers
@@ -1903,6 +1905,8 @@ pulls.recently_pushed_new_branches = You pushed on branch <strong>%[1]s</strong>
 
 pull.deleted_branch = (deleted):%s
 
+comments.edit.already_changed = Unable to save changes to the comment. It appears the content has already been changed by another user. Please refresh the page and try editing again to avoid overwriting their changes
+
 milestones.new = New Milestone
 milestones.closed = Closed %s
 milestones.update_ago = Updated %s