fix: logic of security.md retrieval

prowler/providers/github/services/repository/repository_service.py

@@ -17,7 +17,15 @@ class Repository(GithubService):
         try:
             for repo in self.client.get_user().get_repos():
                 try:
-                    securitymd_exists = repo.get_contents("SECURITY.md") is not None
+                    securitymd_exists = False
+                    contents = repo.get_contents("")
+                    while contents:
+                        file_content = contents.pop(0)
+                        if file_content.type == "dir":
+                            contents.extend(repo.get_contents(file_content.path))
+                        elif file_content.path.endswith("SECURITY.md"):
+                            securitymd_exists = True
+                            break
                 except Exception:
                     securitymd_exists = False
                 repos[repo.id] = Repo(