Fuzz error: correctness/lossless_cast

[mcourteaux]

HL_JIT_TARGET=wasm-32-wasmrt-wasm_simd128
HL_TARGET=wasm-32-wasmrt-wasm_simd128
#CTEST_RESOURCE_GROUP_COUNT=
/Users/halidenightly/build_bot/worker/halide-testbranch-main-llvm_main-x86-64-osx-cmake/halide-build/test/correctness/correctness_lossless_cast
Assertion failed: (isa<To>(Val) && "cast<Ty>() argument of incompatible type!"), function cast, file Casting.h, line 560.
Fuzz testing with root seed 1769885050

From https://buildbot.halide-lang.org/master/#/builders/260/builds/378