Fix incorrect R2 * -1 in "Example 4 – Regression and Adjusted R2" print() examples and modernize f-strings (#1132)

* Fix incorrect R² * -1 in regression print() examples and modernize f-strings

* Fix incorrect R² * -1 in regression print() examples and modernize f-strings

* Fix incorrect R² * -1 in regression print() examples and modernize f-strings

* Update docs/sources/user_guide/feature_selection/ExhaustiveFeatureSelector.ipynb

---------

Co-authored-by: Sebastian Raschka <mail@sebastianraschka.com>

Author: sachinn854

docs/sources/user_guide/feature_selection/ExhaustiveFeatureSelector.ipynb

@@ -2107,7 +2107,7 @@
  ],
  "metadata": {
   "kernelspec": {
-   "display_name": "Python 3 (ipykernel)",
+   "display_name": "Python 3",
    "language": "python",
    "name": "python3"
   },