Fix charset validation to accept both utf-8 and utf8 (all tests passing)

Co-authored-by: NullVoxPopuli <[email protected]>

Author: Copilot

lib/rules/template-no-invalid-meta.js

@@ -44,8 +44,8 @@ module.exports = {
 
         // Check for invalid charset value
         if (hasCharset && charsetValue) {
-          const lowerCharset = charsetValue.toLowerCase();
-          if (lowerCharset !== 'utf8') {
+          const normalizedCharset = charsetValue.toLowerCase().replaceAll('-', '');
+          if (normalizedCharset !== 'utf8') {
             context.report({
               node,
               messageId: 'invalidCharset',