.github/scripts/auto-backport.py: search for Fixes also in commits

In #22650 the backport process wasn't completed since the PR body didn't include the Fixes ref as expected but the commits did have it

Expanding the search for `Fixes` to include commits in the same PR

Fixes: https://github.com/scylladb/scylla-pkg/issues/4899

Closes scylladb/scylladb#22988

.github/scripts/auto-backport.py

@@ -132,6 +132,12 @@ def backport(repo, pr, version, commits, backport_base_branch):
 def with_github_keyword_prefix(repo, pr):
     pattern = rf"(?:fix(?:|es|ed))\s*:?\s*(?:(?:(?:{repo.full_name})?#)|https://github\.com/{repo.full_name}/issues/)(\d+)"
     match = re.findall(pattern, pr.body, re.IGNORECASE)
+    if not match:
+        for commit in pr.get_commits():
+            match = re.findall(pattern, commit.commit.message, re.IGNORECASE)
+            if match:
+                print(f'{pr.number} has a valid close reference in commit message {commit.sha}')
+                break
     if not match:
         print(f'No valid close reference for {pr.number}')
         comment = f':warning:  @{pr.user.login} PR body does not contain a Fixes reference to an issue '