Drop support for Java 11 and modernize #15

Job	Run time
Build scip-java CLI	2m 37s
gradle-kotlin-okio	4m 36s
gradle-kotlin-flowext	3m 47s
bazel-java-examples	2m 55s
maven-kotlin-json-kotlin-maven	1m 46s
gradle-java21-readiness	1m 41s
gradle-mixed-okio-jmh	4m 34s
maven-java17-spring-boot	2m 48s
	24m 44s

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