Fix GitLab provider to use default branch instead of target branch for repo settings

Author: mrT23

pr_agent/git_providers/gitlab_provider.py

@@ -515,7 +515,8 @@ def get_issue_comments(self):
 
     def get_repo_settings(self):
         try:
-            contents = self.gl.projects.get(self.id_project).files.get(file_path='.pr_agent.toml', ref=self.mr.target_branch).decode()
+            main_branch = self.gl.projects.get(self.id_project).default_branch
+            contents = self.gl.projects.get(self.id_project).files.get(file_path='.pr_agent.toml', ref=main_branch).decode()
             return contents
         except Exception:
             return ""