Update peps/pep-0750.rst

Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>

Author: davepeck

peps/pep-0750.rst

@@ -134,7 +134,7 @@ see the `Raw Template Strings`_ section below for more information.
 The ``Template`` Type
 ---------------------
 
-Template strings evaluate to an instance of a new type, ``<<TBD>>.Template``:
+Template strings evaluate to an instance of a new immutable type, ``<<TBD>>.Template``:
 
 .. code-block:: python