Accept multiple requirements txt

[mkniewallner]

Resolves #137.

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

Handle multiple non-dev requirements.txt files. The default won't change, and it's still possible to pass a single file in both the CLI and pyproject.toml, so it is retro-compatible.

[codecov-commenter]

Codecov Report

Merging #141 (2bf9ce3) into main (ce81ea3) will increase coverage by 0.5%.
The diff coverage is 100.0%.

@@           Coverage Diff           @@
##            main    #141     +/-   ##
=======================================
+ Coverage   95.0%   95.5%   +0.5%     
=======================================
  Files         35      35             
  Lines       1180    1207     +27     
=======================================
+ Hits        1121    1153     +32     
+ Misses        59      54      -5     

Impacted Files	Coverage Δ
deptry/cli_defaults.py	100.0% <ø> (ø)
deptry/dependency_getter/requirements_txt.py	96.5% <100.0%> (+<0.1%)	⬆️
deptry/dependency_specification_detector.py	88.5% <100.0%> (-0.4%)	⬇️
tests/test_cli.py	100.0% <100.0%> (ø)
tests/test_dependency_specification_detector.py	100.0% <100.0%> (+13.8%)	⬆️
tests/test_requirements_txt_dependency_getter.py	100.0% <100.0%> (ø)

Help us with your feedback. Take ten seconds to tell us how you rate us. Have a feature suggestion? Share it here.

[fpgmaas]

Great work, looks good to me!