Merge pull request #1823 from braingram/rtd_dirty_flag

ignore files changed by rtd to fix version

.readthedocs.yaml

@@ -11,6 +11,8 @@ build:
       - git fetch --unshallow || true
       - git config remote.origin.fetch '+refs/heads/*:refs/remotes/origin/*' || true
       - git fetch --all --tags || true
+    pre_install:
+      - git update-index --assume-unchanged docs/rtd_environment.yaml docs/conf.py
 
 conda:
   environment: docs/rtd_environment.yaml