Allow 204 response to OPTIONS request from WebDAV server

https://forums.zotero.org/discussion/101824/possible-to-allow-http-204-response-for-options-request-in-webdav-server-check

The specs used to (seemingly inadvertently) disallow 204 for OPTIONS,
but they've been clarified to make it clear that it's allowed [1], and MDN
now even shows it as an example [2].

[1] https://stackoverflow.com/a/57455110
[2] https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/OPTIONS

chrome/content/zotero/xpcom/storage/webdav.js

@@ -221,6 +221,7 @@ Zotero.Sync.Storage.Mode.WebDAV.prototype = {
 				"OPTIONS",
 				this.rootURI,
 				{
+					successCodes: [200, 204, 404],
 					errorDelayIntervals: this.ERROR_DELAY_INTERVALS,
 					errorDelayMax: this.ERROR_DELAY_MAX,
 				}
@@ -622,7 +623,7 @@ Zotero.Sync.Storage.Mode.WebDAV.prototype = {
 			"OPTIONS",
 			uri,
 			{
-				successCodes: [200, 404],
+				successCodes: [200, 204, 404],
 				requestObserver: function (req) {
 					if (req.channel) {
 						channel = req.channel;