Make the unary operator FloatTy check exhaustive

Add a spot that was missed in
<#121997>.

Author: tgross35

compiler/rustc_const_eval/src/interpret/operator.rs

@@ -433,13 +433,16 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             }
             ty::Float(fty) => {
                 let val = val.to_scalar();
+                if un_op != Neg {
+                    span_bug!(self.cur_span(), "Invalid float op {:?}", un_op);
+                }
+
                 // No NaN adjustment here, `-` is a bitwise operation!
-                let res = match (un_op, fty) {
-                    (Neg, FloatTy::F16) => Scalar::from_f16(-val.to_f16()?),
-                    (Neg, FloatTy::F32) => Scalar::from_f32(-val.to_f32()?),
-                    (Neg, FloatTy::F64) => Scalar::from_f64(-val.to_f64()?),
-                    (Neg, FloatTy::F128) => Scalar::from_f128(-val.to_f128()?),
-                    _ => span_bug!(self.cur_span(), "Invalid float op {:?}", un_op),
+                let res = match fty {
+                    FloatTy::F16 => Scalar::from_f16(-val.to_f16()?),
+                    FloatTy::F32 => Scalar::from_f32(-val.to_f32()?),
+                    FloatTy::F64 => Scalar::from_f64(-val.to_f64()?),
+                    FloatTy::F128 => Scalar::from_f128(-val.to_f128()?),
                 };
                 Ok(ImmTy::from_scalar(res, layout))
             }