bpo-46662: Fix convert_timestamp function that failed to correctly parse timestamp

[Rayologist]

This change fixes convert_timestamp() function by splitting timezone information and time

https://bugs.python.org/issue46662

[the-knights-who-say-ni]

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[erlend-aasland]

If this is to be applied, we need test cases for it and a NEWS entry.

[bedevere-bot]

Most changes to Python require a NEWS entry.

Please add it using the blurb_it web app or the blurb command-line tool.

[erlend-aasland]

The default converters and adapters were deprecated in gh-90016. This implies we won't accept this PR, but thank you nonetheless for your interest in improving CPython! We added recipes for common converters and adapters to the sqlite3 docs. You might want to take a look at those.

Thanks!