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.

routers/web/feed/convert.go

@@ -297,7 +297,8 @@ func releasesToFeedItems(ctx *context.Context, releases []*repo_model.Release) (
 
 		link := &feeds.Link{Href: rel.HTMLURL()}
 		content, err = markdown.RenderString(&markup.RenderContext{
-			Ctx: ctx,
+			Ctx:  ctx,
+			Repo: rel.Repo,
 			Links: markup.Links{
 				Base: rel.Repo.Link(),
 			},