Docs: Add missing void to DocBlock @return types.

This commit adds missing `void` return types to (parent) methods that can ''explicitly'' return `void` as one of their conditional paths.

Addressed methods:
* `WP_Privacy_Requests_Table::column_status()`
* `WP_Recovery_Mode::handle_error()`
* `WP_Widget::form()` — unlike the others, it's the ''child'' classes that return `void` when the method is correctly implemented.

Note: `@return void` (where `void` is the single type returned) should not be used outside the default bundled themes and the PHP compatibility shims included in WordPress Core, as per the [https://developer.wordpress.org/coding-standards/inline-documentation-standards/php/ documentation standards].

Follow-up to [30382], [42967], [43256], [44973], [45448].

Props justlevine.
See #52217, #62281.

git-svn-id: https://develop.svn.wordpress.org/trunk@59336 602fd350-edb4-49c9-b593-d223f7449a82

Author: SergeyBiryukov

src/wp-admin/includes/class-wp-privacy-requests-table.php

@@ -430,7 +430,8 @@ public function column_cb( $item ) {
 	 * @since 4.9.6
 	 *
 	 * @param WP_User_Request $item Item being shown.
-	 * @return string Status column markup.
+	 * @return string|void Status column markup. Returns a string if no status is found,
+	 *                     otherwise it displays the markup.
 	 */
 	public function column_status( $item ) {
 		$status        = get_post_status( $item->ID );

src/wp-includes/class-wp-recovery-mode.php

@@ -161,9 +161,9 @@ public function is_initialized() {
 	 * @since 5.2.0
 	 *
 	 * @param array $error Error details from `error_get_last()`.
-	 * @return true|WP_Error True if the error was handled and headers have already been sent.
-	 *                       Or the request will exit to try and catch multiple errors at once.
-	 *                       WP_Error if an error occurred preventing it from being handled.
+	 * @return true|WP_Error|void True if the error was handled and headers have already been sent.
+	 *                            Or the request will exit to try and catch multiple errors at once.
+	 *                            WP_Error if an error occurred preventing it from being handled.
 	 */
 	public function handle_error( array $error ) {
 

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

@@ -138,7 +138,7 @@ public function update( $new_instance, $old_instance ) {
 	 * @since 2.8.0
 	 *
 	 * @param array $instance The settings for the particular instance of the widget.
-	 * @return string Default return is 'noform'.
+	 * @return string|void Default return is 'noform'.
 	 */
 	public function form( $instance ) {
 		echo '<p class="no-options-widget">' . __( 'There are no options for this widget.' ) . '</p>';