tdf#115084: fix sloppy mnemonic ID

Change-Id: I8f9df0baa2862eefada8fafeb384e0129df3f7e9
Reviewed-on: https://gerrit.libreoffice.org/50839Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Katarina Behrens <Katarina.Behrens@cib.de>

cui/uiconfig/ui/optuserpage.ui

@@ -860,7 +860,7 @@
                     <property name="halign">end</property>
                     <property name="label" translatable="yes" context="optuserpage|signingkeylabel">OpenPGP signing key:</property>
                     <property name="use_underline">True</property>
-                    <property name="mnemonic_widget">encryptionkey</property>
+                    <property name="mnemonic_widget">signingkey</property>
                   </object>
                   <packing>
                     <property name="left_attach">0</property>