I noticed a small test hole in codecov: we weren't testing
Temporal.Instant parsing with trailing zeroes in the offset.
I also didn't see fractional offset testing, so added that too.
See https://github.com/tc39/proposal-temporal/pull/2397
Adds tests for ISO strings with named and numeric offset time zone
annotations, with and without the critical flag, with various combinations
of Z and offset in front of the annotation.