write to env file instead of setenv

main.go

@@ -155,7 +155,22 @@ func setOutput(k, v string) (err error) {
 		return errors.Wrap(err, "write to output")
 	}
 
-	os.Setenv(k, v)
+	envFilepath := os.Getenv("GITHUB_ENV") + eol
+
+	envFile, err := os.OpenFile(envFilepath, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0o644)
+	if err != nil {
+		return errors.Wrap(err, "open env file")
+	}
+
+	defer func() {
+		if cErr := envFile.Close(); cErr != nil && err == nil {
+			err = cErr
+		}
+	}()
+
+	if _, err := envFile.Write([]byte(msg)); err != nil {
+		return errors.Wrap(err, "write to env file")
+	}
 
 	return nil
 }