Help: s/unusedVars/unusedCli/

This was a mistake in the documentation.

Fixes: #21303

Help/manual/cmake-presets.7.rst

@@ -248,7 +248,7 @@ Format
         An optional boolean. Setting this to ``true`` is equivalent to passing
         ``--warn-uninitialized`` on the command line.
 
-      ``unusedVars``
+      ``unusedCli``
 
         An optional boolean. Setting this to ``false`` is equivalent to passing
         ``--no-warn-unused-cli`` on the command line.