fix(components): fix title prop null check in DropdownMenu (#19139)

This PR fixes the logic for nullish `title` prop in `DropdownMenu`,
changing the check from `title !== null` to `title != null`, such that
an undefined title results in this condition evaluating to `false`. The
result is that when `title` is undefined, there will be no 8px spacing
above the clickable dropdown box.

Closes RQA-4497

Author: ncdiehl11

components/src/molecules/DropdownMenu/index.tsx

@@ -260,7 +260,7 @@ export function DropdownMenu(props: DropdownMenuProps): JSX.Element {
       gridGap={SPACING.spacing8}
       width={width}
     >
-      {title !== null ? (
+      {title != null ? (
         <Flex gridGap={SPACING.spacing8} alignItems={ALIGN_CENTER}>
           <StyledText
             desktopStyle="bodyDefaultRegular"