[html5] support hr-in-select

<hr> is not accepted as a valid child of <select>

Reduced test-case

<select>
  <option>A</option>
  <hr>
  <option>B</option>
</select>

Configuration

Use html-validate --print-config FILENAME or show the content of all relevant .htmlvalidate.json files.

{
  "rules": {
    "element-permitted-content": "error"
  }
}

Expected result

No error; see https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/Elements/select#select_with_grouping_options

Actual result

Error: <hr> element is not permitted as content under <select>

Version

• html-validate: 10.3.0
• html-validate-angular:
• html-validate-vue:
• html-validate-protractor: . any other relevant plugin: