Swap macos-13 → -15-intel runners in CI

Adapt to deprecation of macos-13 runners (actions/runner-images#13046).

Author: khaeru

.github/workflows/pytest.yaml

@@ -52,7 +52,7 @@ jobs:
 
     strategy:
       matrix:
-        os: [ macos-13, macos-latest, ubuntu-latest, windows-latest ]
+        os: [ macos-15-intel, macos-latest, ubuntu-latest, windows-latest ]
     runs-on: ${{ matrix.os }}
     steps:
     - uses: francisbilham11/action-cached-lfs-checkout@v3
@@ -88,7 +88,7 @@ jobs:
     strategy:
       matrix:
         os:
-        - macos-13
+        - macos-15-intel
         - macos-latest
         - ubuntu-latest
         - windows-latest
@@ -112,9 +112,9 @@ jobs:
         - { os: macos-latest, version: { upstream: v3.8.0 }}
         - { os: macos-latest, version: { upstream: v3.9.0 }}
         # Redundant with macos-latest
-        - { os: macos-13, version: { upstream: v3.10.0 }}
-        - { os: macos-13, version: { upstream: v3.11.0 }}
-        - { os: macos-13, version: { upstream: main }}
+        - { os: macos-15-intel, version: { upstream: v3.10.0 }}
+        - { os: macos-15-intel, version: { upstream: v3.11.0 }}
+        - { os: macos-15-intel, version: { upstream: main }}
 
       fail-fast: false