src/utils: add ensureError() function

Typescript v4.4 no longer assumes that the error in catch is an Error
object [1]. This adds a helper function to ensure that caught errors
at least match the Error interface. If not, it creates a new Error
object with the value as the message.

[1]: https://devblogs.microsoft.com/typescript/announcing-typescript-4-4-beta/#using-unknown-in-catch-variables

src/ble-pybricks-service/sagas.ts

@@ -12,7 +12,7 @@ import {
     takeEvery,
 } from 'typed-redux-saga/macro';
 import { Action } from '../actions';
-import { hex } from '../utils';
+import { ensureError, hex } from '../utils';
 import {
     BlePybricksServiceActionType,
     BlePybricksServiceCommandAction,
@@ -101,7 +101,7 @@ function* decodeResponse(action: BlePybricksServiceDidNotifyEventAction): Genera
                 );
         }
     } catch (err) {
-        yield* put(eventProtocolError(err));
+        yield* put(eventProtocolError(ensureError(err)));
     }
 }