community: prevent gitlab commit on main branch for Gitlab tool (#27750)

### About

- **Description:** In the Gitlab utilities used for the Gitlab tool
there is no check to prevent pushing to the main branch, as this is
already done for Github (for example here:
https://github.com/lorenzb07/langchain/blob/5a2cfb49e045988d290a1c7e3a0c589d6b371694/libs/community/langchain_community/utilities/github.py#L587).
This PR add this check as already done for Github.
- **Issue:** None
- **Dependencies:** None

libs/community/langchain_community/utilities/gitlab.py

@@ -207,6 +207,12 @@ def create_file(self, file_query: str) -> str:
         Returns:
             str: A success or failure message
         """
+        if self.gitlab_branch == self.gitlab_base_branch:
+            return (
+                "You're attempting to commit directly"
+                f"to the {self.gitlab_base_branch} branch, which is protected. "
+                "Please create a new branch and try again."
+            )
         file_path = file_query.split("\n")[0]
         file_contents = file_query[len(file_path) + 2 :]
         try:
@@ -253,6 +259,12 @@ def update_file(self, file_query: str) -> str:
         Returns:
             A success or failure message
         """
+        if self.gitlab_branch == self.gitlab_base_branch:
+            return (
+                "You're attempting to commit directly"
+                f"to the {self.gitlab_base_branch} branch, which is protected. "
+                "Please create a new branch and try again."
+            )
         try:
             file_path = file_query.split("\n")[0]
             old_file_contents = (
@@ -299,6 +311,12 @@ def delete_file(self, file_path: str) -> str:
         Returns:
             str: Success or failure message
         """
+        if self.gitlab_branch == self.gitlab_base_branch:
+            return (
+                "You're attempting to commit directly"
+                f"to the {self.gitlab_base_branch} branch, which is protected. "
+                "Please create a new branch and try again."
+            )
         try:
             self.gitlab_repo_instance.files.delete(
                 file_path, self.gitlab_branch, "Delete " + file_path