Update theme.json

The theme is currently applying Rubik as a default by mistake. This replaces it with Helvetica.

sunderland/theme.json

@@ -1233,7 +1233,7 @@
 			},
 			"heading": {
 				"typography": {
-					"fontFamily": "var(--wp--preset--font-family--rubik)",
+					"fontFamily": "var(--wp--preset--font-family--helvetica)",
 					"fontStyle": "normal",
 					"fontWeight": "700",
 					"lineHeight": "1.125"
@@ -1277,4 +1277,4 @@
 	],
 	"version": 2,
 	"$schema": "https://schemas.wp.org/trunk/theme.json"
-}
+}