[lucet-wasi-fuzz] use a fixed seed for the fuzzer in `make test`
[lucet-wasi-fuzz] use a fixed seed for the fuzzer in `make test`

The use of the fuzzer in this make target is to prevent bitrot of the fuzzer, not meant to actually
find bugs, so fixing its value doesn't hurt and makes it more deterministic.

fastly/lucet,fastly/lucet,fastly/lucet,fastly/lucet,fastly/lucet