Is the Content-Type header needed in pat-calendar requests

[ale-rt]

We are currently facing an issue with Zope refusing to respond to pat-calendar ajax calls, see plone/plone.restapi#1611.

I think the Content-Type header is not needed here:

Patterns/src/pat/calendar/calendar.js

Lines 311 to 318 in 7e391d3

	response = await fetch(url, {
	method: "GET",
	mode: "cors",
	headers: {
	"Accept": "application/json",
	"Content-Type": "application/json",
	},
	});