Issue #3510868: PHP 8.1 compatibility fix.

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Closes #3510868

src/Plugin/Linkit/Matcher/CKEditorAnchorLinkMatcher.php

@@ -22,7 +22,7 @@ class CKEditorAnchorLinkMatcher extends MatcherBase {
   public function execute($string) {
     $suggestions = new SuggestionCollection();
 
-    $string = ltrim($string, '#');
+    $string = ltrim((string) $string, '#');
 
     $suggestion = new DescriptionSuggestion();
     $suggestion->setLabel($this->t('#@anchor_link', ['@anchor_link' => $string]))