Add attributes to text field template input when using WP Job Manager Field Editor

functions.php

<?php

add_filter( 'field_editor_text_field_attributes', 'smyles_add_text_field_attr', 10, 4 );

function smyles_add_text_field_attr( $attr, $key, $field, $value ){

	if( $key === 'some_meta_key' ){
		// Add readonly attribute (replacing any others added through this filter)
		$attr = 'readonly="readonly"';
	}

	return $attr;
}

If using WP Job Manager Field Editor 1.8.5 OR OLDER you need to update the template file here:
https://gist.github.com/tripflex/063f4e7463a0d270a1f717fd4939531d