Bump checkstyle from 8.29 to 8.30 (JabRef#6051)

Bumps [checkstyle](https://github.com/checkstyle/checkstyle) from 8.29 to 8.30.
- [Release notes](https://github.com/checkstyle/checkstyle/releases)
- [Commits](checkstyle/checkstyle@checkstyle-8.29...checkstyle-8.30)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

build.gradle

@@ -213,7 +213,7 @@ dependencies {
     testImplementation "org.testfx:testfx-junit5:4.0.17-alpha-SNAPSHOT"
     testImplementation "org.hamcrest:hamcrest-library:2.2"
 
-    checkstyle 'com.puppycrawl.tools:checkstyle:8.29'
+    checkstyle 'com.puppycrawl.tools:checkstyle:8.30'
     xjc group: 'org.glassfish.jaxb', name: 'jaxb-xjc', version: '2.3.2'
     jython 'org.python:jython-standalone:2.7.1'
 }