Lexical Analysis ref doc: Fix a typo in the string concatenation internal link (GH-5157)

In lexical analysis reference documentation, the internal link to
the string literal concatenation section was written as`.. _string-catenation:`.
Changed that to `.. _string-concatenation:`.

Doc/reference/lexical_analysis.rst

@@ -571,7 +571,7 @@ that a single backslash followed by a newline is interpreted as those two
 characters as part of the literal, *not* as a line continuation.
 
 
-.. _string-catenation:
+.. _string-concatenation:
 
 String literal concatenation
 ----------------------------