🧪💅 Merge GIL and no-GIL macOS CI definitions

It is a DRY exercise, they were almost the same and there is no reason
to keep them separate in YAML.

.github/workflows/build.yml

@@ -199,53 +199,37 @@ jobs:
       free-threading: ${{ matrix.free-threading }}
 
   build_macos:
-    name: 'macOS'
+    name: >-
+      macOS
+      ${{ fromJSON(matrix.free-threading) && '(free-threading)' || '' }}
     needs: check_source
     if: needs.check_source.outputs.run_tests == 'true'
     strategy:
       fail-fast: false
       matrix:
         # Cirrus and macos-14 are M1, macos-13 is default GHA Intel.
+        # macOS 13 only runs tests against the GIL-enabled CPython.
         # Cirrus used for upstream, macos-14 for forks.
         os:
         - ghcr.io/cirruslabs/macos-runner:sonoma
         - macos-14
         - macos-13
         is-fork:  # only used for the exclusion trick
         - ${{ github.repository_owner != 'python' }}
+        free-threading:
+        - false
+        - true
         exclude:
         - os: ghcr.io/cirruslabs/macos-runner:sonoma
           is-fork: true
         - os: macos-14
           is-fork: false
+        - os: macos-13
+          free-threading: true
     uses: ./.github/workflows/reusable-macos.yml
     with:
       config_hash: ${{ needs.check_source.outputs.config_hash }}
-      os: ${{ matrix.os }}
-
-  build_macos_free_threading:
-    name: 'macOS (free-threading)'
-    needs: check_source
-    if: needs.check_source.outputs.run_tests == 'true'
-    strategy:
-      fail-fast: false
-      matrix:
-        # Cirrus and macos-14 are M1.
-        # Cirrus used for upstream, macos-14 for forks.
-        os:
-        - ghcr.io/cirruslabs/macos-runner:sonoma
-        - macos-14
-        is-fork:  # only used for the exclusion trick
-        - ${{ github.repository_owner != 'python' }}
-        exclude:
-        - os: ghcr.io/cirruslabs/macos-runner:sonoma
-          is-fork: true
-        - os: macos-14
-          is-fork: false
-    uses: ./.github/workflows/reusable-macos.yml
-    with:
-      config_hash: ${{ needs.check_source.outputs.config_hash }}
-      free-threading: true
+      free-threading: ${{ matrix.free-threading }}
       os: ${{ matrix.os }}
 
   build_ubuntu:
@@ -583,7 +567,6 @@ jobs:
     - check-docs
     - check_generated_files
     - build_macos
-    - build_macos_free_threading
     - build_ubuntu
     - build_ubuntu_free_threading
     - build_ubuntu_ssltests
@@ -618,7 +601,6 @@ jobs:
             && '
             check_generated_files,
             build_macos,
-            build_macos_free_threading,
             build_ubuntu,
             build_ubuntu_free_threading,
             build_ubuntu_ssltests,