Fix formatting: Separate Scheme Programming Language editions into distinct entries (#12923)

Co-authored-by: harir03 <[email protected]>

Author: harir03

books/free-programming-books-langs.md

@@ -2446,7 +2446,8 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Scheme Tutorial](http://www.cs.hut.fi/Studies/T-93.210/schemetutorial/)
 * [Simply Scheme: Introducing Computer Science](http://www.cs.berkeley.edu/~bh/ss-toc2.html) - B. Harvey, M. Wright
 * [Teach Yourself Scheme in Fixnum Days](https://ds26gte.github.io/tyscheme/index-Z-H-1.html)
-* [The Scheme Programming Language: Edition 3](http://www.scheme.com/tspl3/) - [The Scheme Programming Language: Edition 4](http://www.scheme.com/tspl4/)
+* [The Scheme Programming Language: Edition 3](http://www.scheme.com/tspl3/)
+* [The Scheme Programming Language: Edition 4](http://www.scheme.com/tspl4/)
 * [Write Yourself a Scheme in 48 Hours](https://en.wikibooks.org/wiki/Write_Yourself_a_Scheme_in_48_Hours) - Wikibooks