use rbenv+ruby-build instead of rvm #325

Job	Run time
build image (x86-mingw32)	1m 46s
build image (x64-mingw-ucrt)	1m 48s
build image (x64-mingw32)	1m 32s
build image (x86-linux)	21m 50s
build image (x86_64-linux)	10m 51s
build image (x86_64-darwin)	15m 52s
build image (arm64-darwin)	16m 15s
build image (arm-linux)	1m 19s
build image (aarch64-linux)	1m 13s
build image (jruby)	26s
multiarch (${{ matrix.platform }} on ${{ matrix.from_image }})	0s
native static	0s
source gem	0s
native	0s
	1h 12m 52s

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