fix(files): add optional ref parameter for cli project-file raw (python-gitlab#3032)

The 
ef parameter was removed in python-gitlab v4.8.0.  This will add 
ef back as an optional parameter for the project-file raw cli command.

Author: ebishop

gitlab/v4/objects/files.py

@@ -277,6 +277,7 @@ def delete(  # type: ignore[override]
     @cli.register_custom_action(
         cls_names="ProjectFileManager",
         required=("file_path",),
+        optional=("ref",),
     )
     @exc.on_http_error(exc.GitlabGetError)
     def raw(

tests/functional/cli/test_cli_files.py

@@ -0,0 +1,21 @@
+def test_project_file_raw(gitlab_cli, project, project_file):
+    cmd = ["project-file", "raw", "--project-id", project.id, "--file-path", "README"]
+    ret = gitlab_cli(cmd)
+    assert ret.success
+    assert "Initial content" in ret.stdout
+
+
+def test_project_file_raw_ref(gitlab_cli, project, project_file):
+    cmd = [
+        "project-file",
+        "raw",
+        "--project-id",
+        project.id,
+        "--file-path",
+        "README",
+        "--ref",
+        "main",
+    ]
+    ret = gitlab_cli(cmd)
+    assert ret.success
+    assert "Initial content" in ret.stdout