Fix ambiguous tests for ensemble max_samples & bootstrap

[PSSF23]

Describe the bug

In some tests for ensembles, such as test_max_samples_boundary_regressors and test_max_samples_boundary_classifiers, the bootstrap parameter is not specified. Yet for some of the estimators tested, they have bootstrap=False by default, including ExtraTreesClassifier, ExtraTreesRegressor and more.

Related to #21294

Steps/Code to Reproduce

Simplified e.g.

test_max_samples_boundary_regressors(ExtraTreesRegressor)

Expected Results

Some error is thrown due to bootstrap=False.

Actual Results

The test pass without errors.

Versions

System:
    python: 3.8.5 (default, Sep  4 2020, 02:22:02)  [Clang 10.0.0 ]
executable: /Users/pssf23/miniconda3/envs/ndd/bin/python
   machine: macOS-10.16-x86_64-i386-64bit

Python dependencies:
          pip: 20.3.3
   setuptools: 58.2.0
      sklearn: 1.0
        numpy: 1.19.5
        scipy: 1.7.1
       Cython: 0.29.21
       pandas: 1.2.0
   matplotlib: 3.3.3
       joblib: 1.0.0
threadpoolctl: 2.1.0

Built with OpenMP: True

[PSSF23]

Take

[glemaitre]

I remove the bug tag because this is just that the parameter is ignored. It is stated in the documentation but could be improved of course.

[PSSF23]

@glemaitre Sure! I updated my comment to include more reasons on the improvement.