Fix get_user_description in case pr_description.enable_pr_type=false

Fixes an issue when getting the user description after a PR-Agent description was already generated, in case the configuration setting `pr_description.enable_pr_type` was `false`.

pr_agent/git_providers/git_provider.py

@@ -107,7 +107,7 @@ def get_pr_description(self, *, full: bool = True) -> str:
     def get_user_description(self) -> str:
         description = (self.get_pr_description_full() or "").strip()
         # if the existing description wasn't generated by the pr-agent, just return it as-is
-        if not description.startswith("## PR Type"):
+        if not any(description.startswith(header) for header in ("## PR Type", "## PR Description")):
             return description
         # if the existing description was generated by the pr-agent, but it doesn't contain the user description,
         # return nothing (empty string) because it means there is no user description