[Type] Mark LGraphGroup.color as optional

[huchenlei]

The LGraphGroup.color can be deleted here. Marking it as optional.

litegraph.js/src/LGraphCanvas.ts

Lines 1436 to 1448 in aafd720

	const fApplyColor = function (node: LGraphNode) {
	if (color) {
	if (node instanceof LGraphGroup) {
	node.color = color.groupcolor
	} else {
	node.color = color.color
	node.bgcolor = color.bgcolor
	}
	} else {
	delete node.color
	delete node.bgcolor
	}
	}