Adding two new Python books by Al Sweigart (#8682)

* chore(deps): bump tj-actions/changed-files from 30.0.0 to 32.1.1

Bumps [tj-actions/changed-files](https://github.com/tj-actions/changed-files) from 30.0.0 to 32.1.1.
- [Release notes](https://github.com/tj-actions/changed-files/releases)
- [Changelog](https://github.com/tj-actions/changed-files/blob/main/HISTORY.md)
- [Commits](https://github.com/tj-actions/changed-files/compare/v30.0.0...v32.1.1)

---
updated-dependencies:
- dependency-name: tj-actions/changed-files
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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* Add Python PDF book from Al Sweigart

* Add online book about python recursion

* undo bot commit

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

books/free-programming-books-langs.md

@@ -1966,6 +1966,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [Python Programming](https://en.wikibooks.org/wiki/Python_Programming) - Wikibooks (2.7)
 * [Python Programming](https://upload.wikimedia.org/wikipedia/commons/9/91/Python_Programming.pdf) - Wikibooks (PDF) (2.6)
 * [Python Programming And Numerical Methods: A Guide For Engineers And Scientists](https://pythonnumericalmethods.berkeley.edu/notebooks/Index.html) - Qingkai Kong, Timmy Siauw, Alexandre Bayen (3.7)
+* [Python Programming Exercises, Gently Explained](https://inventwithpython.com/PythonProgrammingExercisesGentlyExplained.pdf) - Al Sweigart (PDF)
 * [Python Tutorial](https://www.tutorialspoint.com/python/) - Tutorials Point (HTML, PDF)
 * [Scientific Visualization: Python + Matplotlib](https://github.com/rougier/scientific-visualization-book) - Nicolas P. Rougier (PDF)
 * [Scipy Lecture Notes](http://scipy-lectures.github.io)
@@ -1981,6 +1982,7 @@ That section got so big, we decided to split it into its own file, the [BY SUBJE
 * [The Programming Historian](http://niche-canada.org/research/niche-digital-infrastructure-project/the-programming-historian/) - William J. Turkel, Adam Crymble and Alan MacEachern
 * [The Python GTK+ 3 Tutorial](http://python-gtk-3-tutorial.readthedocs.org/en/latest/)
 * [The Python Handbook](https://flaviocopes.com/page/python-handbook/) - Flavio Copes (PDF, EPUB, Kindle) *(email address requested)*
+* [The Recursive Book of Recursion](https://inventwithpython.com/recursion/) - Al Swigart (HTML) (3.x)
 * [The Standard Python Library](https://web.archive.org/web/20200626001242/http://effbot.org/librarybook/) - Fredrik Lundh
 * [Think Complexity](https://greenteapress.com/wp/think-complexity-2e/) - Allen B. Downey (2nd Edition) (PDF, HTML)
 * [Think DSP - Digital Signal Processing in Python](https://greenteapress.com/wp/think-dsp/) - Allen B. Downey (PDF, HTML)