fix(ci): migrate to the latest macOS runners (#8335)

* fix(ci): replace retiring macOS 14 runners

Use the supported macOS 15 ARM64 image before the November 2 retirement. Keep the Intel release runner and existing test/build/release commands unchanged.

* fix(ci): use the latest macOS runner images

.github/workflows/ci.yml

@@ -281,10 +281,10 @@ jobs:
   # otherwise has no server-test coverage. Scoped to the observer/watcher suites to
   # bound runtime.
   server-tests-macos:
-    name: server-tests (macos-14, file observation)
+    name: server-tests (macos-latest, file observation)
     needs: changes
     if: ${{ !cancelled() && (needs.changes.outputs.full != 'false' || needs.changes.outputs.server != 'false') }}
-    runs-on: macos-14
+    runs-on: macos-latest
     steps:
       - uses: actions/checkout@v4
 

.github/workflows/desktop-release.yml

@@ -100,10 +100,10 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - runner: macos-14
+          - runner: macos-latest
             electron_arch: arm64
             node_heap_mb: 4096
-          - runner: macos-15-intel
+          - runner: macos-26-intel
             electron_arch: x64
             node_heap_mb: 8192
     permissions:

.github/workflows/nix.yml

@@ -101,7 +101,7 @@ jobs:
         run: nix build .#desktop -o result-desktop
 
   build-desktop-darwin:
-    runs-on: macos-14
+    runs-on: macos-latest
     steps:
       - uses: actions/checkout@v4