refactor: use generic types instead of typing

[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

Since PEP 585 implemented in Python 3.9, generic types can be used for type annotations in replacement of their counterparts in typing module.

deptry supports Python >= 3.7, but thanks to from __future__ import annotations, it's possible to use those generic types on 3.7+.

[codecov-commenter]

Codecov Report

Merging #217 (3574c57) into main (ea7ba57) will decrease coverage by 0.4%.
The diff coverage is 95.8%.

@@           Coverage Diff           @@
##            main    #217     +/-   ##
=======================================
- Coverage   96.2%   95.7%   -0.5%     
=======================================
  Files         31      31             
  Lines        897     912     +15     
  Branches     201     203      +2     
=======================================
+ Hits         863     873     +10     
- Misses        22      26      +4     
- Partials      12      13      +1     

Impacted Files	Coverage Δ
...ptry/imports/extractors/python_import_extractor.py	100.0% <ø> (ø)
...ry/imports/extractors/notebook_import_extractor.py	88.0% <66.6%> (-12.0%)	⬇️
deptry/cli.py	93.6% <100.0%> (ø)
deptry/config.py	100.0% <100.0%> (ø)
deptry/core.py	97.5% <100.0%> (ø)
deptry/dependency.py	91.2% <100.0%> (ø)
deptry/dependency_getter/base.py	95.0% <100.0%> (ø)
deptry/dependency_getter/pdm.py	100.0% <100.0%> (ø)
deptry/dependency_getter/pep_621.py	92.8% <100.0%> (ø)
deptry/dependency_getter/poetry.py	100.0% <100.0%> (ø)
... and 14 more

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