minor #11213 grammar typo (michaelKaefer)

This PR was submitted for the 4.2 branch but it was merged into the 3.4 branch instead (closes #11213).

Discussion
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grammar typo

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Commits
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3be0563 grammar typo

Author: javiereguiluz

session/locale_sticky_session.rst

@@ -13,7 +13,7 @@ in the session, so that it's used on subsequent requests.
 Creating a LocaleSubscriber
 ---------------------------
 
-Create and a :ref:`new event subscriber <events-subscriber>`. Typically, ``_locale``
+Create a :ref:`new event subscriber <events-subscriber>`. Typically, ``_locale``
 is used as a routing parameter to signify the locale, though you can determine the
 correct locale however you want::