ValueError during timestamp parsing in rare case

[wjh18]

Describe the bug
Discovered a (rare?) bug whereby the API response contains an analysisUTCTimestamp field with no trailing fractions of a second. When converting the timestamp to a Python datetime object in this scenario, it causes: ValueError: time data '2023-03-29T07:09:31Z' does not match format '%Y-%m-%dT%H:%M:%S.%fZ'.

To Reproduce
Can reproduce in testing by supplying api.response._get_timestamp with a mock JSON response dict (should contain a top-level analysisUTCTimestamp item with no trailing fractions of a second in its value). Then assert that it raises ValueError.

Expected behavior
Fractions of a second aren't used in report generation anyway so we should handle both scenarios gracefully (optional %f?).

[wjh18]

Fixed in 9b1291e by removing fractions from timestamps before calling datetime.strptime on timestamp