Downgrade JRuby to 9.x to fix issue with the Rough highlighter on macOS

Reference: asciidoctor/asciidoctorj-pdf#113

Author: marcphilipp

gradle/libs.versions.toml

@@ -10,7 +10,7 @@ eclipse = "4.37.0"
 jackson = "2.20.0"
 jacoco = "0.8.13"
 jmh = "1.37"
-jruby = "10.0.2.0"
+jruby = "9.4.14.0"
 junit4 = "4.13.2"
 junit4Min = "4.12"
 ktlint = "1.7.1"