Add test coverage for required argument validation on builtin components

The rule already had logic to check that required arguments are present
(e.g., LinkTo requires at least one of @route, @query, @model, or @models),
but this code path had no test coverage. Add test cases for both GJS and HBS
parsers to verify that <LinkTo /> without any required argument correctly
reports a requiredArgument error.

Co-Authored-By: Claude Opus 4.6 (1M context) <[email protected]>

Author: NullVoxPopuli

tests/lib/rules/template-no-unknown-arguments-for-builtin-components.js

@@ -184,6 +184,31 @@ ruleTester.run('template-no-unknown-arguments-for-builtin-components', rule, {
       output: null,
       errors: [{ messageId: 'unknownArgument' }],
     },
+
+    // Missing required arguments
+    {
+      code: '<template><LinkTo /></template>',
+      output: null,
+      errors: [{ messageId: 'requiredArgument' }],
+    },
+    {
+      code: '<template><LinkTo @disabled={{true}} /></template>',
+      output: null,
+      errors: [{ messageId: 'requiredArgument' }],
+    },
+    {
+      filename: 'my-component.gjs',
+      code: `
+        import Component from '@glimmer/component';
+        export default class MyComponent extends Component {
+          <template>
+            <LinkTo @replace={{true}}>Home</LinkTo>
+          </template>
+        }
+      `,
+      output: null,
+      errors: [{ messageId: 'requiredArgument' }],
+    },
   ],
 });
 
@@ -333,5 +358,37 @@ Instead, please use the {{on}} modifier, i.e. "<Textarea {{on "keyup" ...}} />"
         },
       ],
     },
+
+    // Missing required arguments
+    {
+      code: '<LinkTo />',
+      output: null,
+      errors: [
+        {
+          message:
+            'Arguments "@route" or "@query" or "@model" or "@models" is required for <LinkTo /> component.',
+        },
+      ],
+    },
+    {
+      code: '<LinkTo @disabled={{true}} />',
+      output: null,
+      errors: [
+        {
+          message:
+            'Arguments "@route" or "@query" or "@model" or "@models" is required for <LinkTo /> component.',
+        },
+      ],
+    },
+    {
+      code: '<LinkTo @replace={{true}}>Home</LinkTo>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Arguments "@route" or "@query" or "@model" or "@models" is required for <LinkTo /> component.',
+        },
+      ],
+    },
   ],
 });