Speed up initial docs generation by setting the git clone depth to 1. (#2093)

* Speed up initial docs cloning

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: alexgmin

docs/management/commands/update_docs.py

@@ -358,7 +358,17 @@ def update_git(self, url, destdir, changed_dir="."):
                 os.chdir(cwd)
         else:
             subprocess.check_call(
-                ["git", "clone", "--branch", branch, repo, str(destdir), quiet],
+                [
+                    "git",
+                    "clone",
+                    "--depth",
+                    "1",
+                    "--branch",
+                    branch,
+                    repo,
+                    str(destdir),
+                    quiet,
+                ],
                 stderr=sys.stdout,
             )
         return True