minor symfony#8646 Change some 3.3 docs to be gender-neutral (javiereguiluz)

This PR was merged into the 3.3 branch.

Discussion
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Change some 3.3 docs to be gender-neutral

This is a continuation of symfony#8645 for newer docs.

Commits
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abe19b7 Change some 3.3 docs to be gender-neutral

Author: wouterj

reference/configuration/security.rst

@@ -478,7 +478,7 @@ dn_string
 **type**: ``string`` **default**: ``{username}``
 
 This is the string which will be used as the bind DN. The ``{username}``
-placeholder will be replaced with the user-provided value (his login).
+placeholder will be replaced with the user-provided value (their login).
 Depending on your LDAP server's configuration, you may need to override
 this value.