Specify version of css_parser

Author: jvgeiger

.github/workflows/build-release-docs.yaml

@@ -33,6 +33,7 @@ jobs:
       - name: Install Asciidoctor-PDF
         run: |
           gem install public_suffix -v 5.1.1
+          gem install css_parser -v 1.17.1
           gem install asciidoctor-pdf
           asciidoctor-pdf --version