Coding Standards: Use a more meaningful variable name in WP_List_Table::months_dropdown().

As per the [https://developer.wordpress.org/coding-standards/wordpress-coding-standards/php/#naming-conventions Naming Conventions]:
> Don't abbreviate variable names unnecessarily; let the code be unambiguous and self-documenting.

Follow-up to [8646], [15491].

See #62279.

git-svn-id: https://develop.svn.wordpress.org/trunk@59755 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/class-wp-list-table.php

@@ -763,11 +763,11 @@ protected function months_dropdown( $post_type ) {
 			return;
 		}
 
-		$m = isset( $_GET['m'] ) ? (int) $_GET['m'] : 0;
+		$selected_month = isset( $_GET['m'] ) ? (int) $_GET['m'] : 0;
 		?>
 		<label for="filter-by-date" class="screen-reader-text"><?php echo get_post_type_object( $post_type )->labels->filter_by_date; ?></label>
 		<select name="m" id="filter-by-date">
-			<option<?php selected( $m, 0 ); ?> value="0"><?php _e( 'All dates' ); ?></option>
+			<option<?php selected( $selected_month, 0 ); ?> value="0"><?php _e( 'All dates' ); ?></option>
 		<?php
 		foreach ( $months as $arc_row ) {
 			if ( 0 === (int) $arc_row->year ) {
@@ -779,7 +779,7 @@ protected function months_dropdown( $post_type ) {
 
 			printf(
 				"<option %s value='%s'>%s</option>\n",
-				selected( $m, $year . $month, false ),
+				selected( $selected_month, $year . $month, false ),
 				esc_attr( $arc_row->year . $month ),
 				/* translators: 1: Month name, 2: 4-digit year. */
 				sprintf( __( '%1$s %2$d' ), $wp_locale->get_month( $month ), $year )