change the github action to use requirments.txt

Author: timtogan

.github/workflows/docs.yml

@@ -13,7 +13,7 @@ jobs:
         with:
           python-version: '3.12'
 
-      - run: pip install mkdocs mkdocs-material mdx_math
+      - run: pip install -r requirements.txt
 
       - run: mkdocs build