Docs: Keep the full month number type for WP_Locale::get_month().

Unlike the other `WP_Locale` getters, `get_month()` returns an empty string for
a month number that is not found, which was added so that callers like
`single_month_title()` can pass unvalidated query var values. Narrowing its
parameter to valid month numbers told callers to validate input the method
already handles, surfacing errors at call sites that pass `zeroise()` results,
query vars, or database values.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: westonruter

src/wp-includes/class-wp-locale.php

@@ -318,8 +318,6 @@ public function get_weekday_abbrev( $weekday_name ) {
 	 *
 	 * @param string|int $month_number '01' through '12'.
 	 * @return string Translated full month name. If the month number is not found, an empty string is returned.
-	 *
-	 * @phpstan-param int<1, 12>|'1'|'2'|'3'|'4'|'5'|'6'|'7'|'8'|'9'|'10'|'11'|'12'|'01'|'02'|'03'|'04'|'05'|'06'|'07'|'08'|'09' $month_number
 	 */
 	public function get_month( $month_number ) {
 		$month_number = zeroise( $month_number, 2 );