[5.7] Set TOOLCHAIN_CHANNEL to 5.7

Author: kateinoigakukun

.github/workflows/build-toolchain.yml

@@ -179,7 +179,7 @@ jobs:
 
   build-toolchain:
     env:
-      TOOLCHAIN_CHANNEL: DEVELOPMENT
+      TOOLCHAIN_CHANNEL: 5.7
       DEVELOPER_DIR: /Applications/Xcode_13.0.app/Contents/Developer/
     needs: [build-matrix]
     if: ${{ always() }}