Make sure to actually use yarn to install the main-packages, otherwise the packages.json#resolutions property will not be used and @babel/helpers would not get overruled

Overruled @babel/helpers to fix how initializers play with decorated properties. Thus circumventing the imperformant and lengthy code being generated by babel in the non-legacy option.

packages/babel-helpers/test/fixtures/dependencies/rename-binding-equal/output.js

@@ -0,0 +1,9 @@
+let _foo = "main";
+
+function _$_renameBindingEqual_main() { return _$_renameBindingEqual_dependency() + _foo; }
+
+let foo = "dependency";
+
+function _$_renameBindingEqual_dependency() { return foo; }
+
+_$_renameBindingEqual_main;