Add MACOSX_DEPLOYMENT_TARGET to macos workflow
diff --git a/.github/workflows/macos.yml b/.github/workflows/macos.yml
index a22a9bb..411cfe1 100644
--- a/.github/workflows/macos.yml
+++ b/.github/workflows/macos.yml
@@ -18,6 +18,8 @@
 
     - name: Build ninja
       shell: bash
+      env:
+        MACOSX_DEPLOYMENT_TARGET: 10.12
       run: |
         cmake -DCMAKE_BUILD_TYPE=Release -B build
         cmake --build build --parallel --config Release