linting: Recheck PR info if it's mergeability is not determined yet.

conda_forge_webservices/linting.py

@@ -4,6 +4,7 @@
 import shutil
 import tempfile
 import textwrap
+import time
 
 import requests
 from git import Repo
@@ -27,7 +28,11 @@ def compute_lint_message(repo_owner, repo_name, pr_id):
     owner = gh.get_user(repo_owner)
     repo = owner.get_repo(repo_name)
 
-    pull_request = repo.get_pull(pr_id)
+    mergeable = None
+    while mergeable is None:
+        pull_request = repo.get_pull(pr_id)
+        mergeable = pull_request.mergeable
+        time.sleep(0.1)
 
     with tmp_directory() as tmp_dir:
         repo = Repo.clone_from(repo.clone_url, tmp_dir)
@@ -38,7 +43,7 @@ def compute_lint_message(repo_owner, repo_name, pr_id):
         sha = str(repo.head.object.hexsha)
 
         # Raise an error if the PR is not mergeable.
-        if not pull_request.mergeable:
+        if not mergeable:
             message = textwrap.dedent("""
                 Hi! This is the friendly automated conda-forge-linting service.