fix escape chars for gh action?

Author: geofffranks

.github/workflows/publish-cpan.yml

@@ -13,7 +13,7 @@ jobs:
       - uses: actions/checkout@v2
       - name: update-version
         run: |
-          sed -i "s/^\$VERSION = '.*';/\$VERSION = '${GITHUB_REF}';/" lib/Test/MockModule.pm
+          sed -i "s/^\\\$VERSION = '.*';/\\\$VERSION = '${GITHUB_REF}';/" lib/Test/MockModule.pm
       - uses: cucumber/[email protected]
         with:
           cpan-user: ${{ secrets.CPAN_USER }}