Build and test Pekko with Scala 3 #619

Job	Run time
Test (;testkit/test;actor-tests/test)	7m 1s
Test (;actor-testkit-typed/test;actor-typed-tests/test)	6m 21s
Test (;bench-jmh/test)	5m 12s
Test (;cluster/test;cluster-tools/test;cluster-typed/test;distributed-data/test;cluster-metrics/t...	18m 54s
Test (;discovery/test;coordination/test)	3m 33s
Test (;persistence/test;persistence-shared/test;persistence-query/test;persistence-typed/test;per...	10m 45s
Test (;pki/test;slf4j/test)	2m 12s
Test (;serialization-jackson/test)	3m 40s
Test (;stream/test;stream-testkit/test;stream-tests/test;stream-typed/test;stream-typed-tests/test)	17m 37s
Test (;stream-tests-tck/test)	5m 38s
Test (;remote/test;remote-tests/test;protobuf-v3/test)	11m 38s
	1h 32m 31s

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