Add JDK 21 to test workflow #80

Job	Run time
build	30s
test-eclipse (eclipse-oxygen)	38s
docker-integration-test (8, maven, mvn compile)	47s
test-eclipse (eclipse-202006)	58s
test-javac (11, javacCurrent)	56s
docker-integration-test (8, gradle, gradle assemble)	42s
test-eclipse (eclipse-202006-jdk8)	1m 23s
test-javac (12, javacCurrent)	53s
docker-integration-test (8, ant, ant dist)	50s
test-eclipse (eclipse-202212)	43s
test-javac (13, javacCurrent)	1m 9s
docker-integration-test (8, bazel, bazel build //:ProjectRunner)	1m 1s
test-eclipse (eclipse-oxygen-full)	1m 11s
test-javac (14, javacCurrent)	1m 7s
docker-integration-test (11, maven, mvn compile)	33s
test-eclipse (eclipse-2022-03-full)	1m 26s
test-javac (15, javacCurrent)	1m 5s
docker-integration-test (11, gradle, gradle assemble)	52s
test-eclipse (ecj11)	36s
test-javac (16, javacCurrent)	58s
docker-integration-test (11, ant, ant dist)	32s
test-eclipse (ecj14)	51s
test-javac (17, javacCurrent)	1m 3s
docker-integration-test (11, bazel, bazel build //:ProjectRunner)	1m 1s
test-eclipse (ecj16)	41s
test-javac (18, javacCurrent)	1m 11s
docker-integration-test (17, maven, mvn compile)	43s
test-eclipse (ecj19)	42s
test-javac (19, javacCurrent)	58s
docker-integration-test (17, gradle, gradle assemble)	37s
test-javac (20, javacCurrent)	1m 2s
docker-integration-test (17, ant, ant dist)	43s
test-javac (21, javacCurrent)	1m 11s
docker-integration-test (17, bazel, bazel build //:ProjectRunner)	1m 19s
test-javac (11, javac6)	56s
test-javac (11, javac8)	1m 20s
	33m 8s

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