[BUGFIX] Correct an exception message (#1296)

This correction is not worthy of a changelog entry or any tests.

Author: JakeQZ

src/RuleSet/DeclarationBlock.php

@@ -97,7 +97,7 @@ public function setSelectors($selectors, ?CSSList $list = null): void
                     if (!Selector::isValid($selector)) {
                         throw new UnexpectedTokenException(
                             "Selector did not match '" . Selector::SELECTOR_VALIDATION_RX . "'.",
-                            $selectors,
+                            $selector,
                             'custom'
                         );
                     }