ci: using Process workingDirectory instead of flutter -C to set the w…

…orking directory to run pub get

scripts/pub_get.dart

@@ -4,6 +4,6 @@ import 'packages.dart';
 
 void main(List<String> args) {
   for (final package in packages) {
-    Process.runSync('flutter', ['pub', 'get', '-C', package]);
+    Process.runSync('flutter', ['pub', 'get'], workingDirectory: package);
   }
 }