Update python-nbformat to version 5.7.3 / rev 16 via SR 1058566
https://build.opensuse.org/request/show/1058566
by user bnavigator + dimstar_suse
- Update to 5.7.3
* Undeprecate validate(nb, relax_add_props=True) #343 (@minrk)
- Release 5.7.2
* Only require nbformat_minor for v4 #342 (@minrk)