Validate PHPCS rulesets

This is an action for GitHub Actions. It runs xmllint on each listed ruleset file.

    - name: "Validate ruleset"
      uses: "szepeviktor/phpcs-ruleset-validator@v0.4.0"
      with:
        # When you indent with tabs
        # xmllint_indent: "\t"
        xml_ruleset: "RulesetName/ruleset.xml"

You can use any key in with. There are two special keys

1. for non-default PHPCS shema path: xml_phpcs_schema
2. for XML file indentation string: xmllint_indent