Bug 12184: fix typo "retricted" on checkin page

Bug 12184: fix typo "retricted" on checkin page

To test:

[1] Check an item that belongs to a restricted patron and
    specify a non-default return date.
[2] Verify that the warning message contains "restricted"
    rather than "retricted".

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Magnus Enger <digitalutvikling@gmail.com>
Patch applies and makes sense. (I have not checked the actual UI,
but that should not be necessary for such a simple typo correction.)

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>