Optionally run tests with pandas

[basnijholt]

Description

This ensures that the minimal dependencies test runs correctly.
Right now pandas is always installed.

Checklist

• Fixed style issues using pre-commit run --all (first install using pip install pre-commit)
• pytest passed

Type of change

Check relevant option(s).

• Bug fix (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)
• (Code) style fix or documentation update
• This change requires a documentation update

[codecov-commenter]

Codecov Report

Merging #369 (290f744) into master (50fae43) will decrease coverage by 0.08%.
The diff coverage is 100.00%.

❗ Current head 290f744 differs from pull request most recent head 14e6ad8. Consider uploading reports for the commit 14e6ad8 to get more accurate results

@@            Coverage Diff             @@
##           master     #369      +/-   ##
==========================================
- Coverage   80.33%   80.24%   -0.09%     
==========================================
  Files          37       37              
  Lines        5375     5377       +2     
  Branches      979      979              
==========================================
- Hits         4318     4315       -3     
- Misses        890      892       +2     
- Partials      167      170       +3     

Impacted Files	Coverage Δ
adaptive/tests/test_learners.py	98.98% <100.00%> (+<0.01%)	⬆️
adaptive/_version.py	45.61% <0.00%> (-3.51%)	⬇️
adaptive/learner/average_learner1D.py	77.66% <0.00%> (-0.67%)	⬇️
adaptive/learner/learner1D.py	89.13% <0.00%> (-0.25%)	⬇️
adaptive/runner.py	69.28% <0.00%> (+0.68%)	⬆️

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