Add a deprecation warning for using Scala 2.12.4 with Bloop (#3470) #9996

Job	Run time
jvm-tests-1	1h 12m 34s
unit-tests	14m 12s
jvm-tests-2	57m 8s
jvm-tests-3	1h 10m 0s
jvm-tests-4	58m 34s
jvm-tests-5	58m 31s
generate-linux-arm64-native-launcher	6m 37s
generate-linux-launcher	9m 15s
generate-macos-launcher	17m 24s
generate-macos-m1-launcher	15m 9s
generate-mostly-static-launcher	7m 45s
generate-windows-launcher	13m 6s
bloop-memory-footprint	15m 9s
docs-tests	42m 4s
checks	15m 38s
format	41s
generate-static-launcher	7m 50s
test-hypothetical-sbt-export	27s
reference-doc	2m 20s
vc-redist	1m 27s
native-mostly-static-tests-2	35m 13s
native-mostly-static-tests-4	32m 31s
native-mostly-static-tests-3	39m 26s
native-mostly-static-tests-1	43m 2s
native-mostly-static-tests-5	34m 28s
native-static-tests-3	39m 50s
native-static-tests-2	35m 28s
native-static-tests-4	33m 53s
native-static-tests-1	42m 23s
native-static-tests-5	34m 28s
native-linux-tests-3	34m 14s
native-linux-tests-1	33m 4s
native-linux-tests-4	26m 16s
native-linux-tests-5	29m 27s
native-linux-tests-2	28m 40s
native-windows-tests-1	41m 10s
native-windows-tests-3	41m 47s
native-windows-tests-2	35m 25s
native-windows-tests-4	33m 23s
native-windows-tests-5	36m 26s
native-macos-tests-3	57m 2s
native-macos-tests-4	55m 10s
native-macos-tests-2	1h 4m 8s
native-macos-tests-1	1h 18m 29s
native-macos-tests-5	1h 1m 22s
native-macos-m1-tests-1	47m 3s
native-macos-m1-tests-3	2h 0m 17s
native-macos-m1-tests-2	47m 20s
native-macos-m1-tests-4	37m 38s
native-macos-m1-tests-5	39m 26s
publish	0s
launchers	0s
Update packages	0s
Update Windows packages	0s
	1d 6h 4m 20s

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