Add support for macos-15 #1288

Job	Run time
Test BUNDLED WITH Bundler dev	5s
lint	9s
Test with a Bundler pre/rc version	2s
macos-14 2.6	5s
Test gemfile depending on Bundler 1	3s
Test with an exact Bundler version	3s
Test bundler: 1.x for old Ruby	3s
Test rubygems: version noops if the default is newer	2s
Test rubygems: version upgrades RubyGems to that version if the default is older	5s
macos-14 2.7	6s
Test with rails5 gemfile	5s
macos-14 3.0	5s
Test with rails6 gemfile	4s
macos-14 3.1	5s
Test with a major Bundler version	1s
Test rubygems: latest on 3.2	9s
macos-14 3.2	5s
Test with a minor Bundler version	3s
Test rubygems: latest on 3.0	5s
macos-14 3.3	5s
Test rubygems: latest on 2.7	3s
macos-14 ruby-head	5s
Test rubygems: latest on 2.6	3s
macos-14 jruby	4s
Test with no Gemfile	3s
Test rubygems: latest on 2.5	5s
macos-14 jruby-head	4s
Test rubygems: latest on 2.3	10s
macos-14 truffleruby	5s
Test rubygems: latest on 2.0	4s
Test installing a Gemfile with nokogiri on TruffleRuby	3s
macos-14 truffleruby-head	5s
Test rubygems: version uses the Bundler installed by the rubygems update	3s
macos-14 truffleruby+graalvm	5s
Test windows-toolchain: none	10s
macos-14 truffleruby+graalvm-head	6s
macos-15 2.6	4s
macos-15 2.7	4s
macos-15 3.0	4s
macos-15 3.1	4s
macos-15 3.2	4s
macos-15 3.3	3s
macos-15 ruby-head	4s
macos-15 jruby	4s
macos-15 jruby-head	4s
macos-15 truffleruby	4s
macos-15 truffleruby-head	4s
macos-15 truffleruby+graalvm	3s
macos-15 truffleruby+graalvm-head	5s
windows-2019 mingw	10s
windows-2019 mswin	9s
windows-2022 mingw	9s
windows-2022 mswin	10s
windows-2022 ucrt	9s
	4m 26s

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