#1411 Improve macOS CI

* Use same capitalization as GitHub: `macOS-*` is now `macos-*`
* `build-cmake`: Now depends on `build-macos` in addition to `build-linux`
  so that a build failure in `build-macos` will stop this step from
  running, just like already happens for Linux.
* `build-cmake`, `test-c-unix`, `test-cmake`: Run on `macos-13` and
  `macos-latest`. This was running on `macos-14` and `macos-latest`
  which is from when `macos-latest` was still `macos-13`. We keep
  `macos-13` for now since this is still an Intel build while
  `macos-14` and later are Apple Silicon hardware.
* `test-cpp-macos`: Remove `macos-12` as this will be turned off in the
  coming months at GitHub. Add `macos-15` which is in public preview.
  Update Xcode versions to the latest for each major version and run
  some of the older ones on `macos-13` now that `macos-12` is gone.
  Additionally, remove Xcode 13.x as it isn't supported by the
  `setup-xcode` action on `macos-13`.

Information about the pending removal of `macos-12` can be found
here: actions/runner-images#10721

Information about Xcode releases can be found here:
https://xcodereleases.com

.github/workflows/ci.yml

@@ -34,7 +34,7 @@ jobs:
           bake --strict
 
   build-macos:
-    runs-on: macOS-latest
+    runs-on: macos-latest
     timeout-minutes: 30
     strategy:
       fail-fast: false
@@ -198,13 +198,13 @@ jobs:
           bake examples/os_api --strict --cfg release
 
   build-cmake:
-    needs: build-linux
+    needs: [build-linux, build-macos]
     runs-on: ${{ matrix.os }}
     timeout-minutes: 30
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-latest, macOS-latest, macOS-14 ]
+        os: [ ubuntu-latest, macos-13, macos-latest ]
 
     steps:
       - uses: actions/checkout@v4
@@ -508,7 +508,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-latest, macOS-latest, macOS-14 ]
+        os: [ ubuntu-latest, macos-13, macos-latest ]
 
     steps:
       - uses: actions/checkout@v4
@@ -605,10 +605,9 @@ jobs:
       fail-fast: false
       matrix:
         os: 
-          - { version: macOS-12, xcode: '13.1' }
-          - { version: macOS-12, xcode: '14.0' }
-          - { version: macOS-13, xcode: '14.3.1' }
-          - { version: macOS-14, xcode: '15.2' }
+          - { version: macos-13, xcode: '14.3.1' }
+          - { version: macos-14, xcode: '15.4' }
+          - { version: macos-15, xcode: '16.0' }
 
     env:
       CC: clang
@@ -915,7 +914,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ ubuntu-latest, macOS-latest, macOS-14 ]
+        os: [ ubuntu-latest, macos-13, macos-latest ]
 
     steps:
       - uses: actions/checkout@v4