docs(guide): fix expect assertion example in guide for spyOn

[winghouchan]

What does this PR do?

Fixes example with spyOn and assertions. The example failed because the spied function would be called once but the expectation asserted 0 calls.

• Documentation or TypeScript types (it's okay to leave the rest blank in this case)
• Code changes

How did you verify your code works?

1. Create test file with example.
2. Run bun test.

Example test should now pass.

[Electroid]

Nice catch, thanks!