Build and test Pekko with Scala 3 #387

Job	Run time
Test (testkit/test actor-tests/test)	6m 52s
Test (actor-testkit-typed/test actor-typed-tests/test)	6m 29s
Test (bench-jmh/test)	4m 5s
Test (cluster/test cluster-tools/test cluster-typed/test distributed-data/test cluster-metrics/te...	18m 53s
Test (discovery/test coordination/test)	2m 53s
Test (persistence/test persistence-shared/test persistence-query/test persistence-typed/test pers...	11m 4s
Test (pki/test slf4j/test)	2m 40s
Test (serialization-jackson/test)	3m 27s
Test (stream/test stream-testkit/test stream-tests/test stream-typed/test stream-typed-tests/test)	17m 35s
Test (stream-tests-tck/test)	5m 28s
Test (remote/test remote-tests/test protobuf-v3/test)	10m 59s
	1h 30m 25s

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