make fy inherit character

[todo]

grattan/R/append_custom_series.R

Lines 63 to 68 in f1cea8b

	# TODO: make fy inherit character
	if (inherits(.subset2(orig, "fy_year"), "fy") &&
	!inherits(.subset2(custom.series, "fy_year"), "fy")) {
	orig <- copy(orig)[, fy_year := as.character(fy_year)]
	}

---

This issue was generated by todo based on a TODO comment in f1cea8b when #201 was merged. cc @HughParsonage.