test(template-no-empty-headings): pin falsy mustache aria-hidden cases

Adds invalid tests for `aria-hidden={{false}}` and `aria-hidden={{"false"}}`
to lock down that falsy mustache values do not exempt an otherwise-empty
heading.

Author: johanrd

tests/lib/rules/template-no-empty-headings.js

@@ -147,5 +147,17 @@ ruleTester.run('template-no-empty-headings', rule, {
       output: null,
       errors: [{ messageId: 'emptyHeading' }],
     },
+
+    // Falsy mustache aria-hidden values do not exempt the heading.
+    {
+      code: '<template><h1 aria-hidden={{false}}></h1></template>',
+      output: null,
+      errors: [{ messageId: 'emptyHeading' }],
+    },
+    {
+      code: '<template><h1 aria-hidden={{"false"}}></h1></template>',
+      output: null,
+      errors: [{ messageId: 'emptyHeading' }],
+    },
   ],
 });