Add error assertion for test on GetTimestampAtHeight

[colin-axner]

Summary

While reviewing #5806, I noticed that the test (which is moved to 02-client keeper tests) for GetTimestampAtHeight uses expPass instead of expError. This can be updated so the test asserts the expected error to be returned

Should be addressed after merging #5806

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[chandiniv1]

@colin-axner can I work on this issue?

[colin-axner]

Hi @chandiniv1, yes that would be wonderful! Can you wait until #5806 is merged into main? The test is moved around in that pr, so it will be easier to address this issue once that pr is merged

[chandiniv1]

@colin-axner yeah it's fine. I'll wait till that issue got merged

[DimitrisJim]

hm, seems like this is currently being addressed in #6002 as part of a slightly larger PR. Pretty sure @damiannolan just missed this issue being opened (there's been many opened as a result of the 02-client refactor and things might slip through!).

Sorry for that, plenty of other issues abound if you want to pick one up! Thanks again for the offer @chandiniv1!