Fix GitHub Actions git ownership issue

Author: SimonR99

.github/workflows/main.yml

@@ -7,5 +7,7 @@ jobs:
     steps:
     - name: Check out
       uses: actions/checkout@v2
+    - name: Fix git ownership
+      run: git config --global --add safe.directory /github/workspace
     - name: Build and Deploy Nikola
       uses: getnikola/nikola-action@v2