Force wrap col within colgroup

Hi, I'm using html-minifier to handle lit HTML template literal, and define each template source using html as keyword. For some reason, I have to define customer col separately and repeat to render different cols for few times. The following code snippet shows the simplest case I have, the output forces adding colgroup for col, which is not expected.

**source code to be minified**

```javascript
import { html } from 'lit-html';
import {repeat} from 'lit/directives/repeat.js';

export default class MinifyTester {
_renderCol() {
return repeat(this.cols, (col) => html ``);
}
_renderColumnGroup() {
return html`

${this._renderCol()}

`;
}
}
```
**minified output:**

```javascript
import { html } from 'lit-html';
import {repeat} from 'lit/directives/repeat.js';

class MinifyTester {
_renderCol() {
return html``;
}
_renderColumnGroup() {
return html`${this._renderCol()}`;
}
}

export { MinifyTester as default };
```
col element is a special case in htmlparser.js, if there's no colgroup in the same template then have to push one and trigger start with two tags (colgroup & col).

```javascript
if (tagName === 'col' && findTag('colgroup') < 0) {
lastTag = 'colgroup';
stack.push({ tag: lastTag, attrs: [] });
if (handler.start) {
await handler.start(lastTag, [], false, '');
}
}
```
Is any chance to cover this case?
Thanks

Start in htmlparser.js at the special-case handling for a col without a colgroup, then reproduce the issue with the supplied lit-html template and repeat directive. Verify that a col rendered inside an existing colgroup is not wrapped in an extra colgroup, while ordinary col parsing still behaves as expected.

Written by the indexing model from the issue text.