Revert some more change

.github/workflows/main.yml

@@ -20,6 +20,7 @@ concurrency:
 
 env:
   MW_HEADERS_DIR: ${{ github.workspace }}/../mw_headers
+  MACOSX_DEPLOYMENT_TARGET: "10.15"
   ACTION_URL: "https://github.com/Cantera/conda-recipes/actions/runs/${{ github.run_id }}"
   INCOMING_REF: ${{ github.event.inputs.incoming_ref }}
 
@@ -106,13 +107,7 @@ jobs:
       - "post-pending-status"
     strategy:
       matrix:
-        include:
-          - os: windows-2019
-            macosx_deployment_target: null
-          - os: ubuntu-22.04
-            macosx_deployment_target: null
-          - os: macos-13
-            macosx_deployment_target: "10.15"
+        os: [windows-2019, ubuntu-20.04, macos-13]
       fail-fast: false
     outputs:
       job-status: ${{ job.status }}
@@ -126,7 +121,7 @@ jobs:
       id: setup-macos-sdk
       uses: ./.github/actions/setup_macos
       with:
-        macos-sdk-version: ${{ matrix.macosx_deployment_target }}
+        macos-sdk-version: ${{ env.MACOSX_DEPLOYMENT_TARGET }}
       if: runner.os == 'macOS'
     - name: Append to conda build config
       if: runner.os == 'macOS'