(Reuters) - Collapsing demand from rental car companies, corporations and government agencies has sapped U.S. auto sales during the coronavirus pandemic and a recovery will likely be slow, threatening auto workers whose jobs depend on fleet sales.Weak fleet orders are expected to hurt June sales, which automakers will report on Wednesday. Cox Automotive forecasts fleet sales will fall nearly 56% to 1.3 million vehicles after plunging 83% in May and 77% in April.In the short term, fleet sales are..