GC: wasmparser: Fix gc/gc-ref.wat roundtrip test

[imikushin]

Fix gc/gc-ref.wat roundtrip test.

Requires #1059.

[fitzgen]

It seems like the gc-ref.wat test is still failing in CI: https://github.com/bytecodealliance/wasm-tools/actions/runs/5248728965/jobs/9480613647?pr=1062#step:4:629

failed test: tests/local/gc/gc-ref.wat

Caused by:
    0: failed testing the binary output of `wat`
    1: wasm isn't valid
    2: type mismatch: expected (ref $type), found (ref $type) (at offset 0x6b)

[fitzgen]

Ah I see this is built on top of the other PR, nevermind.

[imikushin]

Ah I see this is built on top of the other PR, nevermind.

Yep.

[imikushin]

Now that #1059 is merged, this should successfully pass CI.
cc @fitzgen

[imikushin]

Rebased on top of latest main. Should be ready to merge.

[fitzgen]

Thanks!