docs: fixed git unshallow error

Signed-off-by: annecyh <[email protected]>
(cherry picked from commit 035d14c)

Author: AnneCYH

docs/.readthedocs.yaml

@@ -14,6 +14,7 @@ build:
     pre_install:
     - git fetch --unshallow || true
     post_checkout:
+    - git fetch --unshallow || true
     # Cancel building pull requests when there aren't changed in the docs directory.
     # If there are no changes (git diff exits with 0) we force the command to return with 183.
     # This is a special exit code on Read the Docs that will cancel the build immediately.