Update tests/pass/float_nan.rs

Co-authored-by: Ralf Jung <[email protected]>

tests/pass/float_nan.rs

@@ -1,4 +1,4 @@
-//@only-miri: FIXME: did not get value that should be possible: 0x7fc00000 (NaN: Pos, Quiet, payload = 0x0)
+//@only-miri: real executions don't actively randomize NaNs
 
 #![feature(float_gamma, portable_simd, core_intrinsics)]
 use std::collections::HashSet;