datawrapper: Use dark background in dark mode

At the moment, interactive block components set a white background in
dark mode because interactive embeds are assumed not to handle dark
mode.

This was done in
#10578, later modified
in #10580 to remove
transparency.

This blocks the use of datawrapper’s automatic dark mode, because it
causes it to display dark mode colours on a white background.

This commit changes (only) datawrapper interactive block components to
set a dark background in dark mode, which will let us use datawrapper’s
automatic dark mode.

I wasn’t entirely sure which colours to use: articleBackgroundDark seems
the obvious choice (and is what I’ve gone with), but then why doesn’t
interactiveBlockBackgroundList use articleBackgroundLight?

dotcom-rendering/src/components/InteractiveBlockComponent.importable.tsx

@@ -113,7 +113,11 @@ const wrapperStyle = ({
 	isDatawrapperGraphic: boolean;
 }) => css`
 	${format.theme === ArticleSpecial.Labs ? textSans17 : article17}
-	background-color: ${themePalette('--interactive-block-background')};
+	background-color: ${themePalette(
+		isDatawrapperGraphic
+			? '--interactive-block-background-datawrapper'
+			: '--interactive-block-background',
+	)};
 	min-height: ${getMinHeight(role, loaded)};
 	position: relative;
 	display: flex;

dotcom-rendering/src/palette.ts

@@ -6551,6 +6551,10 @@ const paletteColours = {
 		light: interactiveBlockBackgroundLight,
 		dark: interactiveBlockBackgroundDark,
 	},
+	'--interactive-block-background-datawrapper': {
+		light: interactiveBlockBackgroundLight,
+		dark: articleBackgroundDark,
+	},
 	'--interactive-contents-hover': {
 		light: interactiveContentsHoverLight,
 		dark: interactiveContentsHoverDark,