Avoid the use of IDs to associate labels with forum search field.

We have more than one instance of form-search on a page, resulting
in multiple instances of the same ID. This is invalid HTML and causes
errors in WAVE.

See #3269.

wp-content/themes/openlab/bbpress/form-search.php

@@ -15,8 +15,10 @@
 	<div class="bbp-search-form">
 		<form role="search" method="get" id="bbp-search-form" action="<?php echo esc_url( bp_get_group_permalink( groups_get_current_group() ) ); ?>forum/">
 			<div>
-				<label class="screen-reader-text hidden" for="bbp_search"><?php esc_html_e( 'Search for:', 'bbpress' ); ?></label>
-				<input type="text" value="<?php bbp_search_terms(); ?>" name="bbp_search" id="bbp_search" />
+				<label>
+					<span class="screen-reader-text"><?php esc_html_e( 'Search for:', 'bbpress' ); ?></span>
+					<input type="text" value="<?php bbp_search_terms(); ?>" name="bbp_search" id="bbp_search" />
+				</label>
 				<input class="button" type="submit" id="bbp_search_submit" value="<?php esc_attr_e( 'Search', 'bbpress' ); ?>" />
 			</div>
 		</form>