ci: Update macOS runners / versions

https://github.blog/changelog/2025-09-19-github-actions-macos-13-runner-image-is-closing-down/

- CI: Switch to macOS 15 Intel runner
  (macOS 14 is still tested with Apple Silicon)
- Nightly: Use macOS 15 Intel runner for nightly releases
  (macOS 14 would be better to align with actual Intel releases, but it is
  a -large runner, thus possibly metered)
- Releases: Use macOS 14 for Intel releases
  This is a -large runner, but releases don't happen often.

.github/workflows/ci.yml

@@ -202,16 +202,16 @@ jobs:
           - testenv: py314-pyqt610
             os: ubuntu-24.04
             python: "3.14"
-          ### macOS Ventura
-          - testenv: py314-pyqt610
-            os: macos-13
-            python: "3.14"
-            args: "tests/unit"  # Only run unit tests on macOS
           ### macOS Sonoma (M1 runner)
           - testenv: py314-pyqt610
             os: macos-14
             python: "3.14"
             args: "tests/unit"  # Only run unit tests on macOS
+          ### macOS Sequoia (Intel runner)
+          - testenv: py314-pyqt610
+            os: macos-15-intel
+            python: "3.14"
+            args: "tests/unit"  # Only run unit tests on macOS
           ### Windows
           - testenv: py314-pyqt610
             os: windows-2022

.github/workflows/nightly.yml

@@ -14,7 +14,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: macos-13
+          - os: macos-15-intel
             toxenv: build-release
             name: macos-intel
           - os: macos-14
@@ -23,7 +23,7 @@ jobs:
           - os: windows-latest
             toxenv: build-release
             name: windows
-          - os: macos-13
+          - os: macos-15-intel
             args: --debug
             toxenv: build-release
             name: macos-debug-intel

.github/workflows/release.yml

@@ -153,8 +153,8 @@ jobs:
     strategy:
       matrix:
         include:
-          - os: macos-13
+          - os: macos-14-large  # Intel
-          - os: macos-14
+          - os: macos-14  # Apple Silicon
           - os: windows-2022
           - os: ubuntu-24.04
     runs-on: "${{ matrix.os }}"