CI: Fix "::set-output" deprecation #114

Job	Run time
macos-11 - truffleruby+graalvm-head	6h 0m 14s
macos-12 - truffleruby+graalvm-head	7m 38s
ubuntu-20.04 - truffleruby+graalvm-head	3m 42s
macos-11 - ruby-3.0	34s
macos-11 - ruby-3.1	37s
macos-11 - ruby-3.2	40s
macos-12 - ruby-3.0	46s
macos-12 - ruby-3.1	56s
macos-12 - ruby-3.2	40s
linux-amd64 - ruby-3.0 - gnu	22s
linux-amd64 - ruby-3.0 - musl	6s
linux-arm64 - ruby-3.0 - gnu	4s
linux-arm64 - ruby-3.0 - musl	4s
linux-amd64 - ruby-3.1 - gnu	26s
linux-amd64 - ruby-3.1 - musl	6s
linux-arm64 - ruby-3.1 - gnu	5s
linux-arm64 - ruby-3.1 - musl	7s
linux-amd64 - ruby-3.2 - gnu	21s
linux-amd64 - ruby-3.2 - musl	31s
linux-arm64 - ruby-3.2 - gnu	3s
linux-arm64 - ruby-3.2 - musl	4s
	6h 18m 6s

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