Use yellow if an approved review is stale (#26312)

By using a different color it's clear that the review isn't pointing to
the latest commit.

**Screenshots:**
Not stale review:

![image](https://github.com/go-gitea/gitea/assets/1135157/2901ad69-e0d8-4041-b760-277d02dafd45)
Stale review:

![image](https://github.com/go-gitea/gitea/assets/1135157/500b306e-a994-42d4-a2fd-1174774ba5ee)

fixes #26306

Author: sebastian-sauer

models/issues/review.go

@@ -192,6 +192,9 @@ func (r *Review) LoadAttributes(ctx context.Context) (err error) {
 func (r *Review) HTMLTypeColorName() string {
 	switch r.Type {
 	case ReviewTypeApprove:
+		if r.Stale {
+			return "yellow"
+		}
 		return "green"
 	case ReviewTypeComment:
 		return "grey"