bump version to 4.6.15 #1870

Job	Run time
supported_jdks (core, 17)	2m 20s
latest_jdk (ubuntu-latest, core)	1m 49s
supported_jdks (core, 18)	2m 0s
latest_jdk (ubuntu-latest, consumer -x :consumer:junit:clojureTest)	3m 10s
supported_jdks (consumer, 17)	3m 43s
latest_jdk (ubuntu-latest, provider)	3m 40s
supported_jdks (consumer, 18)	3m 13s
latest_jdk (ubuntu-latest, pact-specification-test)	1m 29s
supported_jdks (provider, 17)	3m 59s
latest_jdk (windows-latest, core)	2m 52s
supported_jdks (provider, 18)	3m 22s
latest_jdk (windows-latest, consumer -x :consumer:junit:clojureTest)	4m 0s
supported_jdks (pact-specification-test, 17)	1m 48s
latest_jdk (windows-latest, provider)	4m 52s
supported_jdks (pact-specification-test, 18)	4m 24s
latest_jdk (windows-latest, pact-specification-test)	2m 4s
latest_jdk (macos-latest, core)	1m 21s
latest_jdk (macos-latest, consumer -x :consumer:junit:clojureTest)	3m 36s
latest_jdk (macos-latest, provider)	2m 29s
latest_jdk (macos-latest, pact-specification-test)	1m 37s
	57m 48s

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