Update docs.yaml

Author: yaswant

.github/workflows/docs.yaml

@@ -17,6 +17,6 @@ jobs:
       docs-directory: .
 
   deploy:
-    if: ${{ github.repository == 'MetOffice/simulation-systems' }}
+    if: github.ref == 'refs/heads/main'
     needs: build
     uses: MetOffice/growss/.github/workflows/deploy-sphinx-docs.yaml@main