[devX] make labels only count their own occurences (pytorch#98551)

Small QoL improvement such that add_numbered_label now works more intuitively. Now if we push different labels instead of having `[reverted, mergedX2, revertX3, mergedX4, revertedX5, mergedX6]` we have `[reverted, merged, revertX2, mergedX2, revertedX3, mergedX3]`

Pull Request resolved: pytorch#98551
Approved by: https://github.com/huydhn

Author: PaliC

.github/scripts/trymerge.py

@@ -1040,12 +1040,14 @@ def gen_commit_message(self, filter_ghstack: bool = False) -> str:
         return msg
 
     def add_numbered_label(self, label_base: str) -> None:
-        labels = self.get_labels()
-        label = label_base
-        for i in range(len(labels) if labels is not None else 0):
-            if label in labels:
-                label = f"{label_base}X{i+2}"
-        gh_add_labels(self.org, self.project, self.pr_num, [label])
+        labels = self.get_labels() if self.labels is not None else []
+        full_label = label_base
+        count = 0
+        for label in labels:
+            if label_base in label:
+                count += 1
+                full_label = f"{label_base}X{count}"
+        gh_add_labels(self.org, self.project, self.pr_num, [full_label])
 
     def remove_label(self, label: str) -> None:
         if self.get_labels() is not None and label in self.get_labels():