Why my code doesn’t work?

I’m trying to create a function to make bold e-mails in the content of job listings, but it seems not working.

I already tried on the post-type “post” and it works, but when I change to “job_listing”, it seems not working – why is that?

function bold_emails_in_job_listings($content) {
	var_dump(is_singular('job_listing')); 
    if (is_singular('job_listing')) {
        $content = preg_replace_callback('/\b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b/', function($matches) {
            return '<strong>' . $matches[0] . '</strong>';
        }, $content);
    }

    return $content;
}
add_filter('the_content', 'bold_emails_in_job_listings');

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