test

Update installation guide in README post Ruby 4.0.0 release #248

Job	Run time
ruby-versions / Generate Ruby versions	5s
build (2.7 / macos-latest)	30s
build (2.7 / ubuntu-latest)	27s
build (3.2 / macos-latest)	12s
build (2.5 / ubuntu-latest)	20s
build (3.4 / ubuntu-latest)	9s
build (2.6 / ubuntu-latest)	27s
build (3.2 / ubuntu-latest)	9s
build (2.6 / macos-latest)	40s
build (4.0 / ubuntu-latest)	8s
build (3.0 / ubuntu-latest)	8s
build (4.0 / macos-latest)	14s
build (3.1 / ubuntu-latest)	10s
build (3.3 / ubuntu-latest)	12s
build (jruby / macos-latest)	35s
build (head / macos-latest)	10s
build (jruby-head / macos-latest)	39s
build (2.5 / macos-15-intel)	1m 10s
build (jruby / ubuntu-latest)	51s
build (head / ubuntu-latest)	8s
build (3.0 / macos-latest)	16s
build (jruby-head / ubuntu-latest)	50s
build (3.4 / macos-latest)	14s
build (3.1 / macos-latest)	12s
build (3.3 / macos-latest)	11s
	9m 7s

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