Add x86_64-linux as a supported platform

Follow up to: #563
We’re encountering a platform incompatibility error when deploying on Shipit. Its platform is `x86_64-linux` while our bundle currently supports `arm64-darwin-22` only.

<details><summary>Shipit deployment error in question</summary>

```shell
$ bundle install --frozen --jobs 4 --path /app/data/bundler --retry 2
pid: 30136
[DEPRECATED] The `--frozen` flag is deprecated because it relies on being remembered across bundler invocations, which bundler will no longer do in future versions. Instead please use `bundle config set --local frozen 'true'`, and stop using this flag
[DEPRECATED] The `--path` flag is deprecated because it relies on being remembered across bundler invocations, which bundler will no longer do in future versions. Instead please use `bundle config set --local path '/app/data/bundler'`, and stop using this flag
Your bundle only supports platforms ["arm64-darwin-22"] but your local platform
is x86_64-linux. Add the current platform to the lockfile with
`bundle lock --add-platform x86_64-linux` and try again.
```

</details>

I went with the approach of running `bundle lock --add-platform x86_64-linux` as it was what was suggested from the shipit deployment error log. This added the `x86_64-linux` line to the `Gemfile.lock` which was seems to be fairly common in other public libraries under shopify:
  - https://github.com/Shopify/packwerk/blob/main/Gemfile.lock#L181-L185
  - https://github.com/Shopify/rbi/blob/236708902ab30eb23a335221e9a708e8d9b1eb44/Gemfile.lock#L86-L90
  - https://github.com/Shopify/oktakit/blob/17d5feb907c6a43f98bf8d5e543e12d1e4456baf/Gemfile.lock#L65-L68

Gemfile.lock

@@ -84,6 +84,7 @@ GEM
 
 PLATFORMS
  arm64-darwin-22
+ x86_64-linux
 
 DEPENDENCIES
  byebug