Update to JRuby 9.4.3.0

JRuby 9.4.3.0 includes an udpated Psych YAML library, which uses
SnakeYAML-Engine and avoids several CVEs against the original
SnakeYAML. By updating here, downstream users of asciidoctorj will
not run into security audit issues.

See related issues and PRs:

* jruby/jruby#7570
* jruby/jruby#7600
* jruby/jruby#7626
* jruby/jruby#7935

build.gradle

@@ -69,7 +69,7 @@ ext {
   guavaVersion = '18.0'
   hamcrestVersion = '1.3'
   jcommanderVersion = '1.82'
-  jrubyVersion = '9.4.2.0'
+  jrubyVersion = '9.4.3.0'
   jsoupVersion = '1.14.3'
   junitVersion = '4.13.2'
   assertjVersion = '3.19.0'