Fix automerge checks (#4308)

increase per_page for checks query in automerge

Author: balopat

dev_tools/auto_merge.py

@@ -358,8 +358,9 @@ def get_pr_checks(pr: PullRequestDetails) -> Dict[str, Any]:
     References:
         https://developer.github.com/v3/checks/runs/#list-check-runs-for-a-specific-ref
     """
-    url = "https://api.github.com/repos/{}/{}/commits/{}/check-runs?access_token={}".format(
-        pr.repo.organization, pr.repo.name, pr.branch_sha, pr.repo.access_token
+    url = (
+        f"https://api.github.com/repos/{pr.repo.organization}/{pr.repo.name}"
+        f"/commits/{pr.branch_sha}/check-runs?per_page=100&access_token={pr.repo.access_token}"
     )
     response = requests.get(url, headers={'Accept': 'application/vnd.github.antiope-preview+json'})