Update checkstyle (JabRef#12793)

Author: koppor

build.gradle

@@ -400,7 +400,7 @@ dependencies {
     // recommended by https://github.com/wiremock/wiremock/issues/2149#issuecomment-1835775954
     testImplementation 'org.wiremock:wiremock-standalone:3.12.1'
 
-    checkstyle 'com.puppycrawl.tools:checkstyle:10.21.3'
+    checkstyle 'com.puppycrawl.tools:checkstyle:10.21.4'
     // xjc needs the runtime as well for the ant task, otherwise it fails
     xjc group: 'org.glassfish.jaxb', name: 'jaxb-xjc', version: '3.0.2'
     xjc group: 'org.glassfish.jaxb', name: 'jaxb-runtime', version: '3.0.2'