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/user/home.go

@@ -262,6 +262,7 @@ func Milestones(ctx *context.Context) {
 			},
 			Metas: milestones[i].Repo.ComposeMetas(ctx),
 			Ctx:   ctx,
+			Repo:  milestones[i].Repo,
 		}, milestones[i].Content)
 		if err != nil {
 			ctx.ServerError("RenderString", err)