Upgrade from deprecated macos-13 to macos-15-intel in CI

Author: cclauss

.github/workflows/branchbuild.yml

@@ -140,7 +140,7 @@ jobs:
       fail-fast: false
       matrix:
         python-version: ["3.10", "3.11", "3.12", "3.13", "3.13t"]
-        os: [ubuntu-latest, ubuntu-24.04-arm, windows-latest, windows-11-arm, macos-13, macos-14]
+        os: [ubuntu-latest, ubuntu-24.04-arm, windows-latest, windows-11-arm, macos-15-intel, macos-14]
         exclude:
           - python-version: "3.10"
             os: windows-11-arm

.github/workflows/releasebuild.yml

@@ -95,7 +95,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [macos-13, macos-14]
+        os: [macos-15-intel, macos-14]
     env:
       CIBW_TEST_SKIP: "pp*-macosx_*"
       CIBW_BUILD_VERBOSITY: 3