fix: typos in "Named Implementations" (#3296)

* fix: typos in "Named Implementations"

* Update docs/source/tutorial/interfaces.rst

---------

Co-authored-by: G. Allais <guillaume.allais@ens-lyon.org>

docs/source/tutorial/interfaces.rst

@@ -707,7 +707,7 @@ We can define two different implementations of ``Semigroup`` and
 
 The neutral value for addition is ``0``, but the neutral value for multiplication
 is ``1``. It's important, therefore, that when we define implementations
-of ``Monoid`` they extend the correct ``Semigroup`` implementation. We can
+of ``Monoid`` that they extend the correct ``Semigroup`` implementation. We can
 do this with a ``using`` clause in the implementation as follows:
 
 .. code-block:: idris