Correct a typo in the Unittest documentation (GH-10397)

Co-Authored-By: maggyero <gery.ogam@gmail.com>
diff --git a/Doc/library/unittest.rst b/Doc/library/unittest.rst
index c401908..8afbee6 100644
--- a/Doc/library/unittest.rst
+++ b/Doc/library/unittest.rst
@@ -607,7 +607,7 @@
 
 .. versionadded:: 3.4
 
-When some of your tests differ only by a some very small differences, for
+When there are very small differences among your tests, for
 instance some parameters, unittest allows you to distinguish them inside
 the body of a test method using the :meth:`~TestCase.subTest` context manager.