Use monospace font in PR command line instructions (#35074)

Before:

<img width="878" height="426" alt="Screenshot 2025-07-14 at 17 17 11"
src="https://github.com/user-attachments/assets/6e27acb9-bad5-4811-b7b1-5418f0ef12eb"
/>

After:

<img width="878" height="429" alt="Screenshot 2025-07-14 at 17 17 22"
src="https://github.com/user-attachments/assets/b0bd2bfa-e4e2-492a-9c08-66607343a459"
/>

Co-authored-by: Giteabot <teabot@gitea.io>

Author: silverwind

templates/repo/issue/view_content/pull_merge_instruction.tmpl

@@ -7,7 +7,7 @@
 		{{if ne .PullRequest.HeadRepo.ID .PullRequest.BaseRepo.ID}}
 			{{$localBranch = print .PullRequest.HeadRepo.OwnerName "-" .PullRequest.HeadBranch}}
 		{{end}}
-		<div class="ui secondary segment">
+		<div class="ui secondary segment tw-font-mono">
 			{{if eq .PullRequest.Flow 0}}
 			<div>git fetch -u {{if ne .PullRequest.HeadRepo.ID .PullRequest.BaseRepo.ID}}<origin-url data-url="{{.PullRequest.HeadRepo.Link}}"></origin-url>{{else}}origin{{end}} {{.PullRequest.HeadBranch}}:{{$localBranch}}</div>
 			{{else}}
@@ -23,7 +23,7 @@
 				<div>{{ctx.Locale.Tr "repo.pulls.cmd_instruction_merge_warning"}}</div>
 			{{end}}
 		</div>
-		<div class="ui secondary segment">
+		<div class="ui secondary segment tw-font-mono">
 			<div data-pull-merge-style="merge">
 				<div>git checkout {{.PullRequest.BaseBranch}}</div>
 				<div>git merge --no-ff {{$localBranch}}</div>