fix selected state in single date widget (#11955)

DateSingleWidget wasn't explicitly setting itself to not be a range
picker nor were we checking that prop in the css class we applied which
resulted in an inconsistent selected state in the single date widget.

frontend/src/metabase/components/Calendar.jsx

@@ -158,7 +158,10 @@ export default class Calendar extends Component {
     return (
       <div
         className={cx("Calendar Grid-cell", {
-          "Calendar--range": this.props.selected && this.props.selectedEnd,
+          "Calendar--range":
+            this.props.isRangePicker &&
+            this.props.selected &&
+            this.props.selectedEnd,
         })}
       >
         {this.renderMonthHeader(current, side)}

frontend/src/metabase/parameters/components/widgets/DateSingleWidget.jsx

@@ -11,6 +11,7 @@ const DateSingleWidget = ({ value, setValue, onClose }) => {
         initial={value}
         selected={value}
         selectedEnd={value}
+        isRangePicker={false}
         onChange={value => {
           setValue(value);
           onClose();