Ignore tests directory when loading packages

[angrybayblade]

Proposed changes

This issues mentioned below were caused by the check-package not checking the imports in the test directory, this PR adds a flag to check the test dependencies as well

Fixes

fixes #657
fixes #578

Types of changes

What types of changes does your code introduce to agents-aea?
Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply.

• I have read the CONTRIBUTING doc
• I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• Lint and unit tests pass locally with my changes and CI passes too
• I have added tests that prove my fix is effective or that my feature works
• I have checked that code coverage does not decrease.
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

[codecov-commenter]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (2be89a7) 91.99% compared to head (9b7ac05) 91.99%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #676      +/-   ##
==========================================
- Coverage   91.99%   91.99%   -0.01%     
==========================================
  Files         371      371              
  Lines       29539    29541       +2     
==========================================
+ Hits        27175    27176       +1     
- Misses       2364     2365       +1     

Flag	Coverage Δ
unittests	91.99% <100.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
aea/cli/check_packages.py	96.83% <100.00%> (+0.02%)	⬆️

... and 1 file with indirect coverage changes

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[solarw]

lgtm