Fix a typo with Markdown syntax (#3306)

Author: seisman

doc/techref/index.md

@@ -3,7 +3,7 @@
 The Technical Reference section provides detailed information on the technical aspects of
 GMT and PyGMT, including supported encodings, fonts, bit and hachure patterns, and other
 essential components for creating high-quality visualizations. For additional details,
-visit the :gmt-docs:`GMT Technical Reference <reference.html>`.
+visit the {gmt-docs}`GMT Technical Reference <reference.html>`.
 
 ```{toctree}
 :maxdepth: 1