fix calendar not showing events with the same name and start date but different calendar url (#3166)

I fixed the calendar module, which did not show calendar entries from
different calendars that share the same name and start date.

My use case: We have each office days documented in each an own
calendar. If both "Office" Calendar entries start at the same date just
one was shown

Google Calendar (each Office event in an own calendar)

![260753381-c8d5aedf-3c11-4d91-83e8-8549eb261e58](https://github.com/MichMich/MagicMirror/assets/6515818/0cb0ecbd-65bb-4ec4-b5e6-b011cb1c9c6b)

Before

![260751994-b308d549-fcb9-406e-9419-cdd2fed96dc6](https://github.com/MichMich/MagicMirror/assets/6515818/ed4d4645-0852-4e19-99ed-fec3f25d547a)

After

![260753208-3278e32b-9ca5-483a-bc6f-745cbf3964fc](https://github.com/MichMich/MagicMirror/assets/6515818/41b70843-af9f-47fc-baed-91c3c63e9acb)

tests/configs/modules/calendar/show-duplicates-in-calendar.js

@@ -0,0 +1,36 @@
+/* MagicMirror² Test config for multiple calendar events having the same name and start date/time
+ *
+ * By Paranoid93 https://github.com/Paranoid93/
+ * MIT Licensed.
+ */
+let config = {
+	timeFormat: 12,
+
+	modules: [
+		{
+			module: "calendar",
+			position: "bottom_bar",
+			config: {
+				maximumEntries: 30,
+				hideDuplicates: false,
+				calendars: [
+					{
+						maximumEntries: 15,
+						maximumNumberOfDays: 10000,
+						url: "http://localhost:8080/tests/mocks/calendar_test.ics" // contains 11 events
+					},
+					{
+						maximumEntries: 15,
+						maximumNumberOfDays: 10000,
+						url: "http://localhost:8080/tests/mocks/calendar_test_clone.ics" // clone of upper calendar
+					}
+				]
+			}
+		}
+	]
+};
+
+/*************** DO NOT EDIT THE LINE BELOW ***************/
+if (typeof module !== "undefined") {
+	module.exports = config;
+}