fix error catb

Related Issue or bug

Closes #2769

Describe the changes you've made

Running deepcopy(pipeline) on a pipleine containing a catboost model returns the catboost estimator instead of the pipeline self. Very weird. I changed deepcopy for copy, which is fine since the underlying estimators are only used for transform

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Code style update (formatting, local variables)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] This change requires a documentation update