Add post title as a alt for thumbnail

wp_get_attachment_image_attributes.php

<?php
add_filter(
	'wp_get_attachment_image_attributes',
	function( $attr, $attachment, $size ) {
		if ( ! is_singular() ) {
			return $attr;
		}
		if ( isset( $attr['alt'] ) && ! empty( $attr['alt'] ) ) {
			return $attr;
		}
		$attr['alt'] = get_the_title();
		return $attr;
	},
	10,
	3
);