Default macOS CI to macos-26, keep Intel as regression

Move the primary macOS runner to macos-26, the upcoming macos-latest
alias, and run the full Ruby matrix there. RubyGems is a library rather
than the interpreter, so per-OS-version regression adds little; keep
only macos-15-intel on Ruby 4.0 to cover the x86_64 architecture.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: hsbt

.github/workflows/bundler.yml

@@ -35,10 +35,13 @@ jobs:
           - { name: ruby-4.0, value: 4.0.5 }
 
         include:
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: ruby-3.2, value: 3.2.11 }, timeout: 90 }
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: ruby-3.3, value: 3.3.11 }, timeout: 90 }
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: ruby-3.4, value: 3.4.9 }, timeout: 90 }
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: ruby-4.0, value: 4.0.5 }, timeout: 90 }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: ruby-3.2, value: 3.2.11 }, timeout: 90 }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: ruby-3.3, value: 3.3.11 }, timeout: 90 }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: ruby-3.4, value: 3.4.9 }, timeout: 90 }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: ruby-4.0, value: 4.0.5 }, timeout: 90 }
+
+          # Regression coverage for the Intel architecture with the latest Ruby only
+          - { os: { name: macOS-intel, value: macos-15-intel }, ruby: { name: ruby-4.0, value: 4.0.5 }, timeout: 90 }
 
           # Ruby 3.2 is about 20 minutes slower than 3.3/3.4, so it will be excluded from testing.
           - { os: { name: Windows, value: windows-2025 }, ruby: { name: ruby-3.3, value: 3.3.11 }, timeout: 150, group: a }
@@ -55,7 +58,7 @@ jobs:
           - { os: { name: Windows, value: windows-2025 }, ruby: { name: ruby-4.0, value: 4.0.5 }, timeout: 150, group: d }
 
           - { os: { name: Ubuntu, value: ubuntu-24.04 }, ruby: { name: jruby, value: jruby-10.1.0.0 } }
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: jruby, value: jruby-10.1.0.0 } }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: jruby, value: jruby-10.1.0.0 } }
           - { os: { name: Windows, value: windows-2025 }, ruby: { name: jruby, value: jruby-10.1.0.0 } }
 
           - { os: { name: Ubuntu, value: ubuntu-24.04 }, ruby: { name: truffleruby, value: truffleruby-34.0.1 }, timeout: 20 }

.github/workflows/realworld-bundler.yml

@@ -31,10 +31,10 @@ jobs:
           - { name: ruby-4.0, value: 4.0.5 }
 
         include:
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: ruby-3.2, value: 3.2.11 } }
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: ruby-3.3, value: 3.3.11 } }
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: ruby-3.4, value: 3.4.9 } }
-          - { os: { name: macOS, value: macos-15 }, ruby: { name: ruby-4.0, value: 4.0.5 } }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: ruby-3.2, value: 3.2.11 } }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: ruby-3.3, value: 3.3.11 } }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: ruby-3.4, value: 3.4.9 } }
+          - { os: { name: macOS, value: macos-26 }, ruby: { name: ruby-4.0, value: 4.0.5 } }
     env:
       RGV: .
       RUBYOPT: --disable-gems

.github/workflows/rubygems.yml

@@ -27,7 +27,7 @@ jobs:
       matrix:
         os:
           - { name: Ubuntu, value: ubuntu-24.04 }
-          - { name: macOS, value: macos-15 }
+          - { name: macOS, value: macos-26 }
           - { name: Windows, value: windows-2025 }
 
         ruby:
@@ -37,11 +37,15 @@ jobs:
           - { name: "4.0", value: 4.0.5 }
 
         include:
+          # Regression coverage for the Intel architecture with the latest Ruby only
+          - ruby: { name: "4.0", value: 4.0.5 }
+            os: { name: macOS-intel, value: macos-15-intel }
+
           - ruby: { name: jruby, value: jruby-10.1.0.0 }
             os: { name: Ubuntu, value: ubuntu-24.04 }
 
           - ruby: { name: jruby, value: jruby-10.1.0.0 }
-            os: { name: macOS, value: macos-15 }
+            os: { name: macOS, value: macos-26 }
 
           - ruby: { name: jruby, value: jruby-10.1.0.0 }
             os: { name: Windows, value: windows-2025 }