chore(ci): Add an initial delay to let gitflow ci start before checking mergeability (#18383)

I think this action ran through faster than it took the Gitflow PR CI to
start which is why it immediately detected a mergable state and finished
running without reporting an issue.

The action now waits a minute before starting its check.

Closes #18384

Author: andreiborza

.github/workflows/gitflow-merge-conflict.yml

@@ -19,6 +19,7 @@ jobs:
         uses: actions/github-script@v8
         with:
           script: |
+            const initialDelay = 60_000; // Wait 1 minute before first check to let CI start
             const retryInterval = 30_000;
             const maxRetries = 10; // (30 seconds * 10 retries) = 5 minutes
 
@@ -39,6 +40,10 @@ jobs:
             let attempt = 0;
             let mergeable = null;
 
+            // Wait before first check to give CI time to start
+            console.log(`Waiting ${initialDelay/1000} seconds before first check to let CI start...`);
+            await sleep(initialDelay);
+
             while (attempt < maxRetries) {
               attempt++;
               console.log(`Attempt ${attempt}/${maxRetries}: Checking if PR is mergeable...`);