add bandit, a security linter

[skshetry]

See https://github.com/PyCQA/bandit.

[codecov-commenter]

Codecov Report

Base: 81.65% // Head: 80.80% // Decreases project coverage by -0.85% ⚠️

Coverage data is based on head (6622b31) compared to base (d175b92).
Patch coverage: 25.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #150      +/-   ##
==========================================
- Coverage   81.65%   80.80%   -0.86%     
==========================================
  Files          25       25              
  Lines        3396     3396              
  Branches      583      583              
==========================================
- Hits         2773     2744      -29     
- Misses        542      562      +20     
- Partials       81       90       +9     

Impacted Files	Coverage Δ
src/scmrepo/git/backend/pygit2.py	74.50% <0.00%> (-1.99%)	⬇️
src/scmrepo/git/backend/dulwich/credentials.py	25.22% <33.33%> (ø)
src/scmrepo/utils.py	67.74% <0.00%> (-19.36%)	⬇️
tests/conftest.py	86.00% <0.00%> (-9.00%)	⬇️
src/scmrepo/git/backend/gitpython.py	63.34% <0.00%> (-1.08%)	⬇️
src/scmrepo/git/backend/dulwich/__init__.py	78.76% <0.00%> (-0.46%)	⬇️

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