Fix GH actions and readthedocs

Conda has been removed and version.py does not work on GH actions.

.github/workflows/tests.yml

@@ -14,6 +14,11 @@ jobs:
       - name: Set up Git repository
         uses: actions/checkout@v4
 
+      - name: Fetch all Git tags
+        # this is necessary for version.py because git describe does not work on a shallow clone:
+        # https://stackoverflow.com/q/66349002/859591
+        run: git fetch -a
+
       - uses: actions/setup-python@v5
         with:
           python-version: '3.10'

.readthedocs.yaml

@@ -4,15 +4,12 @@
 
 version: 2
 
-build:
-  os: ubuntu-22.04
-  tools:
-    python: "mambaforge-22.9"
-
 sphinx:
   configuration: doc/conf.py
 
-# Python requirements required to build your documentation
-# See https://docs.readthedocs.io/en/stable/guides/reproducible-builds.html
-conda:
-  environment: env.yml
+python:
+  install:
+    - method: pip
+      path: .
+      extra_requirements:
+        - doc