Fix ambiguous shortcut for Ctrl+/

The shortcut was ambiguous because it was active in the button and in the
SQL editor itself. In the button was only documentation and was made
ambiguous when enabling the feature and fixing the shortcut in
6425fb177e

Now its scope is reduced to widget like similar button shortcuts so it can
be unambiguous in the editor.

See issue #1614

src/MainWindow.ui

@@ -2433,6 +2433,9 @@ You can drag SQL statements from the Schema column and drop them into the SQL ed
    <property name="shortcut">
     <string>Ctrl+/</string>
    </property>
+   <property name="shortcutContext">
+    <enum>Qt::WidgetShortcut</enum>
+   </property>
   </action>
   <action name="actionSqlStop">
    <property name="icon">