fix path pattern in documentation pipeline (#919)

Author: dklimpel

.github/workflows/docs.yaml

@@ -7,7 +7,7 @@ on:
   pull_request:
     paths:
       - mkdocs.yml
-      - docs/
+      - docs/**
       - README.md
       - LICENSE
       - extras/**/README.md

.github/workflows/preview-docs.yaml

@@ -5,7 +5,7 @@ on:
       - opened
     paths:
       - mkdocs.yml
-      - docs/
+      - docs/**
       - README.md
       - LICENSE
       - extras/**/README.md