bug(ios): keyboard-loading error message appeared when swapping from sys keyboard to in-app after changing active keyboard

Sentry Issue: [KEYMAN-WEB-K5](https://keyman.sentry.io/issues/5366388113/?referrer=github_integration)

```
Error: Sorry, the US Basic keyboard for English is not currently available.
at (@keymanapp/keyman/web/src/engine/main/src/contextManagerBase.ts:353:46)
```

I (@jahorton) just happened to see this one while trying to reproduce #11532. I first tried using the short-tap described in the issue to change keyboards, but in the system-keyboard context, that just loads the next one in line. After doing that twice, I did a few long-press picker swaps back to the default... then decided to try thing out in-app. I was presented with an error notification once the app loaded. The case I saw does not appear to have passed through to Sentry, though.

What I see via Web inspection:

> (3) keymanweb-webview.js:5898 Uncaught (in promise) Error: Sorry, the ye_old_ten_key keyboard for English is not currently available.
> at keymanweb-webview.js:5898
> at sentryWrapped (sentry.min.js:2)
> (3) keymanweb-webview.js:5898 Uncaught (in promise) Error: Sorry, the gesture_prototyping keyboard for English is not currently available.
> at keymanweb-webview.js:5898
> at sentryWrapped (sentry.min.js:2)

The keyboards mentioned here were the ones reached by short-tap in the system-keyboard context.