[5.0.x] Fixed typo in docs/topics/forms/index.txt.

Backport of 46df3ab244e1688bd186f0bfbfea6a354097a910 from main

docs/topics/forms/index.txt

@@ -594,7 +594,7 @@ required layout. For example:
 By default Django uses the ``"django/forms/field.html"`` template which is
 designed for use with the default ``"django/forms/div.html"`` form style.
 
-The default template can be customized by by setting
+The default template can be customized by setting
 :attr:`~django.forms.renderers.BaseRenderer.field_template_name` in your
 project-level :setting:`FORM_RENDERER`::