fix(pydantic): add upper dependency bound to fix unlocked installations

[yajo]

Fix #1225.

[yajo]

@copier-org/maintainers do you see this as a good temporary fix while we settle #1229?

These months I'll have reduced availability to work on Copier, so I think going for the MVP is a good idea.

[codecov]

Codecov Report

Merging #1244 (77741a6) into master (a5da81c) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1244   +/-   ##
=======================================
  Coverage   96.75%   96.75%           
=======================================
  Files          47       47           
  Lines        3942     3942           
=======================================
  Hits         3814     3814           
  Misses        128      128           

Flag	Coverage Δ
unittests	96.75% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

[sisp]

I'm fine with it. We can move on to Pydantic v2 shortly afterwards. If @pawamoy doesn't have the capacity to finish #1229, I can take over.