Put test dependencies in individual projects

[gdalle]

DI tests

• Stop parsing dependencies from folder names, put them in individual Project.toml files
• Put the test env in the LOAD_PATH first

DI CI

• Adjust names of groups

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 79.16667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 96.57%. Comparing base (0db3be8) to head (438496c).

Files	Patch %	Lines
DifferentiationInterface/test/runtests.jl	70.58%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #361      +/-   ##
==========================================
- Coverage   96.91%   96.57%   -0.34%     
==========================================
  Files         101       98       -3     
  Lines        4824     4813      -11     
==========================================
- Hits         4675     4648      -27     
- Misses        149      165      +16     

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