Arbutus: Remove bottom margin inherited from heading element (#7328)

arbutus/theme.json

@@ -55,6 +55,11 @@
 				}
 			},
 			"core/site-title": {
+				"spacing": {
+					"margin": {
+						"bottom": "0"
+					}
+				},
 				"typography": {
 					"fontSize": "var(--wp--preset--font-size--medium)"
 				}