mrhlpr: Make setting auto merge more robust (MR 38)

Even with the 5 second sleep, it sometimes seems to fail at setting auto
merge, and instead raises GitlabMRClosedError for some reason. As such,
retry up to 3 times with a 5 second sleep in-between, which seems to be
more robust from my testing.

mrhlpr/mr.py

@@ -489,7 +489,15 @@ def finish(
         print("Adding the comment...")
         mr.notes.create({"body": comment})
 
-    # Give gitlab some time to process the push, it sometimes struggles
-    time.sleep(5)
-    print("Setting to auto-merge...")
-    mr.merge(merge_when_pipeline_succeeds=True)
+    # Proper stupid but it works. Originally I had this set to a maximum of 15 seconds
+    # of sleepy time, but for gitlab.com this wasn't always sufficient to catch up.
+    print("Setting to auto-merge (may take up to 25 seconds)...")
+    for _ in range(5):
+        try:
+            # Give gitlab some time to process the push, it sometimes struggles
+            time.sleep(5)
+            mr.merge(merge_when_pipeline_succeeds=True)
+            return
+        except gitlab_api.exceptions.GitlabMRClosedError:
+            pass
+    print("Failed set auto merge! Is the MR open and the GitLab server responsive?")