Add style exception for OOUI buttons' margin

On OOUI forms the text for the checkboxes tended to be rather
misaligned, with the text usually ending up getting shunted off to the
bottom-right corner. It seems the margin being added by the special-case
in this rule was responsible, so I added an exception to it. In testing
things seem to look okay.

Change-Id: Id3ca935e5c83d7c96edcb02d1c6fd72af8e81e58

resources/forms.less

@@ -17,6 +17,11 @@ form {
 		margin: unset;
 		padding: unset;
 	}
+
+	// Padding on checkboxes seems to cause misalignment with its text
+	.oo-ui-checkboxInputWidget input:not( .mw-widgets-datetime-dateTimeInputWidget-editField ):not( .mw-history-compareselectedversions-button ) {
+		margin: unset;
+	}
 }
 
 .oo-ui-buttonElement-framed.oo-ui-labelElement > .oo-ui-buttonElement-button,