Update silencer-lib, silencer-plugin to 1.7.15 (#1648) #2054

Job	Run time
conformance	1m 30s
build (2_12, mima)	1m 3s
build (2_12, e2e)	8s
build (2_12, test)	11m 19s
build (2_13, mima)	1m 16s
build (2_13, e2e)	7s
build (2_13, test)	10m 15s
build (3, mima)	4s
build (3, e2e)	6s
build (3, test)	9m 33s
build (2_12, examples_and_formatting)	2m 33s
build (2_13, scala3_compat_test)	5m 46s
build (3, scala3_compat_test)	8m 24s
ci-passed	1s
	52m 5s

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