fix(Schedule Trigger Node): Follow the correct Unix cron format for month and days of the week (#6401)

* Handle conversion to correct unix format

* Fix intervals, ranges for months

* fix regex to match 10, 11, 12

---------

Co-authored-by: Marcus <marcus@n8n.io>

packages/nodes-base/nodes/Schedule/GenericFunctions.ts

@@ -1,3 +1,4 @@
+import type { IDataObject } from 'n8n-workflow';
 import type { IRecurencyRule } from './SchedulerInterface';
 import moment from 'moment';
 
@@ -55,3 +56,28 @@ export function recurencyCheck(
 	}
 	return false;
 }
+
+export function convertMonthToUnix(expression: string): string {
+	if (!isNaN(parseInt(expression)) || expression.includes('-') || expression.includes(',')) {
+		let matches = expression.match(/([0-9])+/g) as string[];
+		if (matches) {
+			matches = matches.map((match) =>
+				parseInt(match) !== 0 ? String(parseInt(match) - 1) : match,
+			);
+		}
+		expression = matches?.join(expression.includes('-') ? '-' : ',') || '';
+	}
+	return expression;
+}
+
+export function convertToUnixFormat(interval: IDataObject) {
+	const expression = (interval.expression as string).split(' ');
+	if (expression.length === 5) {
+		expression[3] = convertMonthToUnix(expression[3]);
+		expression[4] = expression[4].replace('7', '0');
+	} else if (expression.length === 6) {
+		expression[4] = convertMonthToUnix(expression[4]);
+		expression[5] = expression[5].replace('7', '0');
+	}
+	interval.expression = expression.join(' ');
+}