ci: fix duplicate SDK-update PRs by matching on branch prefix

The existing-PR check filtered by --author 'app/github-actions', but PRs
are created via a GitHub App token (app/reveng-github), so the filter
always matched zero PRs and a new one was opened every run. The title
substring check was also broken (titles are "Update SDK to version X",
not "SDK update X"). Switch to searching open PRs by the sdk-update-
branch prefix, which this workflow itself owns.

Author: robertmarsal

.github/workflows/check.yaml

@@ -51,17 +51,25 @@ jobs:
                 return None
 
         def check_existing_prs():
-            """Check if there are existing open PRs from the bot"""
+            """Check if there are existing open SDK-update PRs.
+
+            Matches by branch prefix `sdk-update-`, which this workflow owns.
+            Author-based filtering is unreliable: PRs are created via a GitHub
+            App token (app/reveng-github), not the default github-actions bot.
+            """
             try:
                 result = subprocess.run([
                     'gh', 'pr', 'list', '--state', 'open',
-                    '--author', 'app/github-actions', '--json', 'title'
+                    '--search', 'head:sdk-update-',
+                    '--json', 'number,title,headRefName'
                 ], capture_output=True, text=True, check=True)
 
                 prs = json.loads(result.stdout)
-                for pr in prs:
-                    if 'SDK update' in pr.get('title', '') or 'OpenAPI' in pr.get('title', ''):
-                        return True
+                matching = [pr for pr in prs if pr.get('headRefName', '').startswith('sdk-update-')]
+                if matching:
+                    for pr in matching:
+                        print(f"  - #{pr['number']} {pr['title']} ({pr['headRefName']})")
+                    return True
                 return False
             except Exception as e:
                 print(f"Error checking existing PRs: {e}")