Update build-mingw.yml

.github/workflows/build-mingw.yml

@@ -26,7 +26,7 @@ jobs:
           git config --global init.defaultBranch master
           cd skia
           rm bin/fetch-gn # not needed and will crash as it's not understanding msys
-          echo "#!/bin/sh\nexit 0\n" > bin/fetch-gn
+          echo "#!#!/usr/bin/env sh\nexit 0\n" > bin/fetch-gn
           echo test:
           bin/fetch-gn
           echo done $?