Bumping version of `wasi` crate dependency (#3476)

## Motivation and Context
The `0.12.0` version of `wasi` suffered from a bug the could impact
users using lower versions of `wit-bindgen` dependencies. Mixed versions
of `wit-bindgen` generated bindings in a single project would cause a
symbol collision. This is fixed by newer versions of `wit-bindgen` and
`wasi = 0.12.1` contains bindings generated by one of these newer
versions. See this issue for details:
https://github.com/bytecodealliance/wit-bindgen/issues/849 and a longer
discussion of the issue on Zulip
[here](https://bytecodealliance.zulipchat.com/#narrow/stream/327223-wit-bindgen/topic/Component.20failing.20to.20compile.20with.20mixed.20wit-bindgen.20versions/near/422068264

).

## Description
<!--- Describe your changes in detail -->
Bumped version of `wasi` dependency in `aws-amithy-wasm` from `0.12.0`
-> `0.12.1`

## Testing
<!--- Please describe in detail how you tested your changes -->
<!--- Include details of your testing environment, and the tests you ran
to -->
<!--- see how your change affects other areas of the code, etc. -->

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [X] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates


----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

---------

Co-authored-by: John DiSanti <john@vinylsquid.com>