Example 4 - Regression and Adjusted R2 - error in print() examples

[rich-ard]

Describe the documentation issue

Code examples in "Example 4 - Regression and adjusted R2" indicate that the R^2 values should be multiplied by -1, which appears to be incorrect (and a result of code reuse from the above Example 3?)

Suggest a potential improvement or addition

Easy fix - I'm happy to check this out and repair it.

At the same time I'm happy to replace the 'old-style' f-string syntax across this section.

[d-kleine]

Also the Boston housing dataset cannot be downloaded anymore with newer sklearn versions via load_boston as this dataset has been removed due to ethical problems: https://scikit-learn.org/1.0/modules/generated/sklearn.datasets.load_boston.html