bug(ios): Sentry upload can fail but CI build continues

@mcdurdin notes while reviewing the build logs of some failed master branch CI builds:

> I note a secondary issue when reviewing the logs -- if sentry upload fails, the build still continues. Can you open an issue on that (and check other platforms? -- macos uploaded successfully, windows had the same error as iOS but failed the build)?
>

>
```
[05:08:17][Step 3/10] warning: sentry-cli - INFO 2021-10-20 05:07:24.246590 +11:00 Loaded config from /.../.sentryclirc
[05:08:17][Step 3/10] INFO 2021-10-20 05:07:24.247352 +11:00 sentry-cli was invoked with the following command line: "sentry-cli" "upload-dif" "/.../keyman/ios/build/Build/Products/Release-iphoneos"
[05:08:17][Step 3/10] error: API request failed
[05:08:17][Step 3/10] caused by: sentry reported an error: bad request (http status: 400)
[05:08:17][Step 3/10] Command PhaseScriptExecution emitted errors but did not return a nonzero exit code to indicate failure