minor #13289 Fix small linguistic error (LauLaman)

This PR was submitted for the 5.0 branch but it was merged into the 4.4 branch instead (closes #13289).

Discussion
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Fix small linguistic error

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Commits
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d7d6c17 Fix small linguistic error

Author: javiereguiluz

security/impersonating_user.rst

@@ -197,8 +197,8 @@ Limiting User Switching
 
 If you need more control over user switching, you can use a security voter. First,
 configure ``switch_user`` to check for some new, custom attribute. This can be
-anything, but *cannot* start with ``ROLE_`` (to enforce that only your voter will)
-be called:
+anything, but *cannot* start with ``ROLE_`` (to enforce that only your voter will 
+be called):
 
 .. configuration-block::