Add Codecov token (required in v4) #190

Job	Run time
build-all	1m 38s
build-java11	1m 18s
tests (core, 8)	1m 2s
tests (driver, 8)	1m 12s
tests (server, 8)	3m 19s
tests (test, 8)	6m 21s
tests (inmemory, -Dtest.skip.tp=false, 8)	30m 47s
tests (berkeleyje, 8)	8m 58s
tests (lucene, 8)	4m 16s
tests (core, -Pjava-11, 11)	1m 9s
tests (driver, -Pjava-11, 11)	58s
tests (server, -Pjava-11, 11)	3m 20s
tests (test, -Pjava-11, 11)	6m 49s
tests (inmemory, -Pjava-11, -Dtest.skip.tp=false, 11)	31m 15s
tests (berkeleyje, -Pjava-11, 11)	9m 0s
tests (lucene, -Pjava-11, 11)	4m 35s
	1h 55m 57s

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