Remove parentheses from tag cloud count

this is an example output of an tag cloud widget element (wp4.8):

<a href="http://localhost/wp-beta-test/tag/handcrafted/" class="tag-cloud-link tag-link-327 tag-link-position-22" style="font-size: 8pt;" aria-label="handcrafted (2 items)">handcrafted<span class="tag-link-count"> (2)</span></a>

as you can see, the widget outputs some aria lable also using parentheses, which interferes with a simple string replace.
the tag number including the parentheses is also already wrapped in a span.

for example, try to use:

function tagcloud_postcount_filter ($variable) {
$variable = str_replace('<span class="tag-link-count"> (', ' <span class="post_count"> ', $variable);
$variable = str_replace(')</span>', '</span>', $variable);
return $variable;
}
add_filter('wp_tag_cloud','tagcloud_postcount_filter');