Unshallow git clone on RTD

Fetch full history so that setuptools-scm could detect correct version

For the context:
- pypa/setuptools_scm#790
- https://docs.readthedocs.io/en/latest/build-customization.html#unshallow-git-clone

.readthedocs.yaml

@@ -17,6 +17,9 @@ build:
   tools:
     python: >-
       3.11
+  jobs:
+    post_checkout:
+      - git fetch --unshallow || true
 
 python:
   install: