Clean gh-pages for repo size

Enable clean and force options for deployment.

Author: henilp105

.github/workflows/build.yml

@@ -65,6 +65,8 @@ jobs:
           token: ${{ secrets.GITHUB_TOKEN }}
           branch: gh-pages
           folder: build/html
-          clean: false
+          clean: true
+          force: true
+          single-commit: true
           git-config-email: 53436240+fortran-lang@users.noreply.github.com
           git-config-name: Fortran