Fix grammar typo in `Doc/c-api/arg.rst` (#130741)

diff --git a/Doc/c-api/arg.rst b/Doc/c-api/arg.rst
index deebaba195299954cee23a5c2910c64ed9ba3fa8..66ccf3c96a65a4fecd9782f5adca6525070d94d0 100644 (file)
--- a/Doc/c-api/arg.rst
+++ b/Doc/c-api/arg.rst
@@ -5,7 +5,7 @@
 Parsing arguments and building values
 =====================================
 
-These functions are useful when creating your own extensions functions and
+These functions are useful when creating your own extension functions and
 methods.  Additional information and examples are available in
 :ref:`extending-index`.