Fix GitHub code scanning alerts in gh-pages workflow

Author: astrovm

.github/workflows/gh-pages.yml

@@ -4,6 +4,9 @@ on:
     branches:
       - master
 
+permissions:
+  contents: write
+
 jobs:
   build:
     name: Deploy docs
@@ -13,7 +16,7 @@ jobs:
         uses: actions/checkout@v3
 
       - name: Deploy docs
-        uses: mhausenblas/mkdocs-deploy-gh-pages@master
+        uses: mhausenblas/mkdocs-deploy-gh-pages@a31c6b13a80e4a4fbb525eeb7a2a78253bb15fa5 # master
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
           CUSTOM_DOMAIN: wiki.anomalous.xyz