ci: allow running the release workflow manually.

Also add the `MACOSX_DEPLOYMENT_TARGET` environment variable while building the Python library.

.github/workflows/release.yaml

@@ -3,6 +3,8 @@ on:
   create:
     tags:
     - 'v*'
+  # Allows you to run this workflow manually from the Actions tab
+  workflow_dispatch:
 jobs:
   build:
     if: ${{ startsWith(github.ref, 'refs/tags/v') }}
@@ -172,6 +174,8 @@ jobs:
         CIBW_TEST_SKIP: '*-macosx_arm64 *-macosx_universal2:arm64'
         CIBW_BUILD_VERBOSITY: 1
 
+        MACOSX_DEPLOYMENT_TARGET: '10.12'
+
     - name: Upload artifacts
       uses: actions/upload-artifact@v4
       with: