style(mypy): silence incorrect typing warnings

[frgfm]

This PR silences the warnings of mypy, which are incorrect

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.75%. Comparing base (71ba1ab) to head (e70d951).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #375   +/-   ##
=======================================
  Coverage   93.75%   93.75%           
=======================================
  Files          62       62           
  Lines        3776     3776           
=======================================
  Hits         3540     3540           
  Misses        236      236           

Files with missing lines	Coverage Δ
holocron/optim/adabelief.py	85.71% <100.00%> (ø)
holocron/optim/adamp.py	88.05% <100.00%> (ø)
holocron/optim/adan.py	88.15% <100.00%> (ø)
holocron/optim/ademamix.py	89.39% <100.00%> (ø)
holocron/optim/wrapper.py	85.60% <ø> (ø)
holocron/trainer/core.py	90.43% <ø> (ø)