gha bootstrap-dev-rhel8: configure git safe.directory (#37702)

git has been updated to something more recent

.github/workflows/valid-style.yml

@@ -72,6 +72,7 @@ jobs:
       - name: Setup repo and non-root user
         run: |
           git --version
+          git config --global --add safe.directory /__w/spack/spack
           git fetch --unshallow
           . .github/workflows/setup_git.sh
           useradd spack-test