With threaded headsets there's very little latitude in fork steerer length. The steerer has to reach into the locknut which has about 8mm of thread, so if you plan to engage at least 4 threads, you only have 3mm to play with.

If your old fork and headset have lots of spacers you plan to remove, or if you're replacing the headset with one have a lower stack height you can shorten the fork accordingly. Otherwise you need to replace with an almost identical fork.

BTW- French made Peugeots use French thread headsets, and a smaller diameter quill stem than standatd (BSC or ISO) so check yours before shopping for replacements, lest you end up spending more chasing compatibility. Fork, then headset, then stem then handlebars.