chore(deps): bump mypy to 1.4.0

[mkniewallner]

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

Description of changes

Bump mypy to 1.4.0, which allow ignoring unused-code reports for more precise ignores (python/mypy#15164).

[codecov]

Codecov Report

Merging #429 (c98fd4a) into main (e274139) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #429   +/-   ##
=====================================
  Coverage   96.2%   96.2%           
=====================================
  Files         38      38           
  Lines       1081    1081           
  Branches     220     220           
=====================================
  Hits        1040    1040           
  Misses        25      25           
  Partials      16      16           

Impacted Files	Coverage Δ
deptry/core.py	97.8% <100.0%> (ø)