The US has declined Poland's offer. Apparently the plan was indeed that Ukrainian pilots should start to missions from Ramstein airbase in 'US' MiG-29 planes that Poland would have given to them. Maybe this plan seemed to spicy even for US warmongers. Also note, that Germany did not protest. The German government knows, that they have no say in this.
No one is wondering, why there where no US planes attacking Assad in Syria.