Auto merge of #1347 - RalfJung:float-cast-test, r=RalfJung
Auto merge of #1347 - RalfJung:float-cast-test, r=RalfJung

rename test_cast -> test_both_cast to make purpose clearer

rust-lang/miri,rust-lang/miri,rust-lang/miri,rust-lang/miri