Only include in versions.toml crates under the sdk directory (#2663)

## Motivation and Context
We have found that `aws-sdk-rust` release-2023-05-01 brought in the
`aws-wasm` crate to `versions.toml`. The crate comes from an example in
the `aws-doc-sdk-examples` repository. This PR fixes gradle build in
`sdk` so that the `publisher` only considers crates under the `sdk`
directory when generating `versions.toml`.

## Testing
Manually ran
```
./gradlew :aws:sdk:assemble
```
and confirmed that `versions.toml` got created under
`smithy-rs/aws/sdk/build/aws-sdk`
~~`smithy-rs/aws/sdk/build/aws-sdk/sdk`~~ and `README` was successfully
hydrated.

----

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choice._

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Co-authored-by: Yuki Saito <awsaito@amazon.com>