Error: Fetch failed with status '502': '' in swaps.utils.js

https://metamask.sentry.io/issues/4363189420/?referrer=github_plugin

```
Error: Fetch failed with status '502': ''
at _default (shared/lib/fetch-with-cache.js:42:11)
at r.fetchTradesInfo (shared/lib/swaps-utils.js:277:9)
at async Promise.all (index 0)
at exports.default.fetchAndSetQuotes (app/scripts/controllers/swaps.js:287:10)
```

Start with the linked Sentry event, then trace the failure through shared/lib/fetch-with-cache.js, shared/lib/swaps-utils.js, and app/scripts/controllers/swaps.js. Determine why the trades-info fetch returns status 502 and what behavior should replace the failure; the issue is done when the cause is resolved and the relevant flow no longer produces this error.

Written by the indexing model from the issue text.