@actions/exec: convert to ESM module

__tests__/scripts/stdoutputspecial.cjs

@@ -0,0 +1,8 @@
+//first half of © character
+process.stdout.write(Buffer.from([0xC2]), (err) => {
+    //write in the callback so that the second byte is sent separately
+    setTimeout(() => {
+        process.stdout.write(Buffer.from([0xA9])) //second half of © character
+    }, 5000)
+   
+})