[CI] macos-13 -> macos-15-intel and bump actions/checkout (#71)

Author: giordano

.github/workflows/ci.yml

@@ -26,14 +26,14 @@ jobs:
           - 'nightly'
         os:
           - ubuntu-latest
-          - macos-13
+          - macos-15-intel
           - windows-latest
         arch:
           - x64
           - x86
         # 32-bit Julia binaries are not available on macOS
         exclude:
-          - os: macOS-13
+          - os: macos-15-intel
             arch: x86
         include:
           - os: macOS-latest
@@ -55,7 +55,7 @@ jobs:
             arch: 'default'
             version: '1.7.3'
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@v2
         with:
           version: ${{ matrix.version }}