update readthedocs

.readthedocs.yml

@@ -2,11 +2,16 @@
 version: 2
 build:
   os: ubuntu-20.04
+  jobs:
+    pre_install:
+        # see https://github.com/readthedocs/readthedocs.org/issues/8201
+      - git update-index --assume-unchanged ci/requirements/docs.yml docs/conf.py
+      # needs to be editable
+      - pip install -e .
   tools:
     python: mambaforge-4.10
 sphinx:
   configuration: docs/conf.py
   fail_on_warning: false
 conda:
   environment: ci/requirements/docs.yml
-formats: []