Bump Buildpacks platform version to `0.12` in build strategy samples #3139

Job	Run time
integration (v1.25.16)	25m 8s
integration (v1.28.6)	24m 54s
e2e (v1.25.16)	24m 57s
test-docker-build (base)	41s
unit	2m 47s
e2e (v1.28.6)	24m 34s
test-docker-build (git)	58s
test-docker-build (image-processing)	58s
test-docker-build (waiter)	42s
	1h 45m 39s

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