Install Ruby 3.4 as baseruby for emscripten builder #616

Job	Run time
ci-data	2s
Compile native gem for aarch64-linux	5m 34s
Compile native gem for aarch64-linux-musl	5m 39s
Compile native gem for arm64-darwin	5m 24s
Compile native gem for x64-mingw-ucrt	5m 45s
Compile native gem for x86_64-darwin	5m 23s
Compile native gem for x86_64-linux	5m 33s
Compile native gem for x86_64-linux-musl	5m 31s
	38m 51s

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