Update build.yml

Author: codeofandrin

.github/workflows/build.yml

@@ -78,7 +78,7 @@ jobs:
         if: matrix.os == 'macos-latest'
         run: |
           cd backend
-          pyinstaller build_mac_arm64.spec
+          python3.9 -m PyInstaller build_mac_arm64.spec
 
       - name: Build backend executable x64
         id: build-backend-x64