Fix documentation style guide formatting

- Correct CPU indentation to 3 spaces
- Correct free-threaded indentation to 3 spaces
- Change 'prevent' to 'avoid' as suggested by reviewer

Author: arunkumargururaj07-star

documentation/style-guide.rst

@@ -77,12 +77,12 @@ C API
   to write extension modules. All caps and unhyphenated.
 
 CPU
-    Central processing unit. No need to spell out.
+   Central processing unit. No need to spell out.
 
 free-threaded
-    The preferred term for the build mode that makes the global interpreter
-    lock (GIL) optional (per :pep:`703`). Avoid using "No-GIL" to prevent
-    double negatives (for example, "non-no-GIL").
+   The preferred term for the build mode that makes the global interpreter
+   lock (GIL) optional (per :pep:`703`). Avoid using "No-GIL" to avoid
+   double negatives (for example, "non-no-GIL").
 
 POSIX
    The name assigned to a particular group of standards. This is always