CI: Fix "::set-output" deprecation #116

Job	Run time
macos-11 - ruby-3.0	1m 32s
macos-11 - ruby-3.1	1m 3s
macos-11 - ruby-3.2	40s
macos-12 - ruby-3.0	40s
macos-12 - ruby-3.1	57s
macos-12 - ruby-3.2	42s
macos-11 - truffleruby+graalvm-head	14m 15s
macos-12 - truffleruby+graalvm-head	6h 0m 13s
ubuntu-20.04 - truffleruby+graalvm-head	5m 7s
linux-amd64 - ruby-3.0 - gnu	44s
linux-amd64 - ruby-3.0 - musl	33s
linux-arm64 - ruby-3.0 - gnu	3m 6s
linux-arm64 - ruby-3.0 - musl	3m 11s
linux-amd64 - ruby-3.1 - gnu	38s
linux-amd64 - ruby-3.1 - musl	29s
linux-arm64 - ruby-3.1 - gnu	3m 58s
linux-arm64 - ruby-3.1 - musl	3m 8s
linux-amd64 - ruby-3.2 - gnu	38s
linux-amd64 - ruby-3.2 - musl	29s
linux-arm64 - ruby-3.2 - gnu	13m 21s
linux-arm64 - ruby-3.2 - musl	13m 57s
	7h 9m 21s

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