[REGRESSION] Parsing timestamps with fractional seconds / microseconds / milliseconds / nanoseconds

[alamb]

Describe the bug
#3801 introduced a regression. Prior to arrow 34 the following timestamp could be parsed:

1969-01-01T00:00:00.1' 

However, after the upgrade it will generate a parse error. This can be worked around by padding the precision to be a whole number of seconds, microseconds, milliseconds, or nanoseconds. For example

1969-01-01T00:00:00.100' 

To Reproduce

Try to parse this as a timestamp:

1969-01-01T00:00:00.1' 

Expected behavior
It should be parsed correctly

Additional context
Found during DataFusion upgrade: apache/datafusion#5441

[tustvold]

label_issue.py automatically added labels {'arrow'} from #3860