fix(component/ErrorBox): correct 'occured' -> 'occurred' fallback message

The fallback Error rectifier in
packages/component/src/ErrorBox.tsx constructed
new Error('Unknown error occured') when the source error was a
non-Error value. The message ends up rendered to end users in the
WebChat error box. String-literal-only change.

Author: SAY-5

packages/component/src/ErrorBox.tsx

@@ -42,7 +42,7 @@ function ErrorBox(props: ErrorBoxProps) {
     if (error instanceof Error) {
       rectifiedError = error;
     } else {
-      rectifiedError = new Error('Unknown error occured');
+      rectifiedError = new Error('Unknown error occurred');
       rectifiedError.cause = error;
     }