Replace macos-release by (parseInt(os.version()) - 9) #1291

Job	Run time
Test with no Gemfile	16s
Test rubygems: version noops if the default is newer	4s
Test rubygems: latest on 3.2	7s
lint	13s
Test rubygems: latest on 3.0	8s
Test BUNDLED WITH Bundler dev	4s
Test rubygems: latest on 2.7	23s
Test rubygems: latest on 2.6	23s
Test with a Bundler pre/rc version	17s
Test rubygems: latest on 2.5	19s
Test gemfile depending on Bundler 1	20s
Test rubygems: latest on 2.3	23s
macos-14 2.6	5s
Test with an exact Bundler version	17s
Test rubygems: latest on 2.0	9s
macos-14 2.7	6s
Test bundler: 1.x for old Ruby	21s
macos-14 3.0	4s
macos-14 3.1	5s
Test with rails5 gemfile	21s
Test rubygems: version upgrades RubyGems to that version if the default is older	20s
Test with a major Bundler version	17s
macos-14 3.2	5s
Test with rails6 gemfile	21s
macos-14 3.3	5s
Test with a minor Bundler version	20s
macos-14 ruby-head	5s
Test installing a Gemfile with nokogiri on TruffleRuby	17s
macos-14 jruby	5s
Test rubygems: version uses the Bundler installed by the rubygems update	9s
macos-14 jruby-head	5s
Test windows-toolchain: none	1m 48s
macos-14 truffleruby	5s
macos-14 truffleruby-head	5s
macos-14 truffleruby+graalvm	4s
macos-14 truffleruby+graalvm-head	4s
macos-15 2.6	4s
macos-15 2.7	4s
macos-15 3.0	4s
macos-15 3.1	4s
macos-15 3.2	5s
macos-15 3.3	3s
macos-15 ruby-head	4s
macos-15 jruby	4s
macos-15 jruby-head	4s
macos-15 truffleruby	3s
macos-15 truffleruby-head	3s
macos-15 truffleruby+graalvm	4s
macos-15 truffleruby+graalvm-head	4s
windows-2019 mingw	1m 11s
windows-2019 mswin	1m 3s
windows-2022 mingw	1m 29s
windows-2022 mswin	2m 3s
windows-2022 ucrt	2m 30s
	17m 46s

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