Use repo as of renderctx's member rather than a repoPath on metas (#29222)

Use a `gitrepo.Repository` in the markup's RenderContext but not store
the repository's path.

services/mailer/mail.go

@@ -220,7 +220,8 @@ func composeIssueCommentMessages(ctx *mailCommentContext, lang string, recipient
 
 	// This is the body of the new issue or comment, not the mail body
 	body, err := markdown.RenderString(&markup.RenderContext{
-		Ctx: ctx,
+		Ctx:  ctx,
+		Repo: ctx.Issue.Repo,
 		Links: markup.Links{
 			AbsolutePrefix: true,
 			Base:           ctx.Issue.Repo.HTMLURL(),