Update macos images for Github Actions to use macos-15

Author: y9v

.github/workflows/nix.yml

@@ -19,10 +19,10 @@ jobs:
         platform:
           - os: darwin
             cpu: x86_64
-            base: macos-13 # always x86_64-darwin
+            base: macos-15-intel # always x86_64-darwin
           - os: darwin
             cpu: arm64
-            base: macos-14 # always arm64-darwin
+            base: macos-15 # always arm64-darwin
           - os: linux
             cpu: x86_64
             base: ubuntu-24.04 # always x86_64-linux-gnu

.github/workflows/test-macos.yaml

@@ -17,18 +17,22 @@ jobs:
       fail-fast: false
       matrix:
         os:
-          - macos-13
+          - macos-15
         ruby:
-          - '2.5'
-          - '2.6'
-          - '2.7'
           - '3.0'
           - '3.1'
           - '3.2'
           - '3.3'
           - '3.4'
           - '3.5'
           # ADD NEW RUBIES HERE
+        include:
+          - os: macos-14
+            ruby: '2.5'
+          - os: macos-14
+            ruby: '2.6'
+          - os: macos-14
+            ruby: '2.7'
     name: Test (${{ matrix.os }}, ${{ matrix.ruby }})
     runs-on: ${{ matrix.os }}
     env: