ci: fix RTD builds when last git tag is more than 50 commits behind

.readthedocs.yml

@@ -10,6 +10,13 @@ build:
   os: ubuntu-22.04
   tools:
     python: "3.11"
+
+  # Unshallow the git clone to allow vcs versioning to pick
+  # up tags properly
+  jobs:
+    post_checkout:
+      - git fetch --unshallow || true
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py