Update documentation in datetime module strftime-and-strptime-behavior fix typo in '%W' format code description (GH-30232)

A small change to the documentation of datetime module , in the format codes section of stftime and strptime. Changed the description of format code '%W' from 'as a decimal number' to 'a zero padded   decimal number' so it's in line with the example having leading zeros.  Similar to the format code '%U' above.

Automerge-Triggered-By: GH:pganssle