bug: karma tests sometimes warn about missing contentId on menu even if present

### Prerequisites

- [X] I have read the [Contributing Guidelines](https://github.com/ionic-team/ionic-framework/blob/main/.github/CONTRIBUTING.md#creating-an-issue).
- [X] I agree to follow the [Code of Conduct](https://ionicframework.com/code-of-conduct).
- [X] I have searched for [existing issues](https://github.com/ionic-team/ionic-framework/issues) that already report this problem, without success.

### Ionic Framework Version

- [ ] v4.x
- [X] v5.x
- [X] v6.x

### Current Behavior

Sometimes when running Karma tests in an Ionic Angular side menu app, Ionic will give the following errors/warnings:

```
ERROR: 'Menu: must have a "content" element to listen for drag events on.'

WARN: 'split pane does not have a specified main node'
```

This is happening even if `contentId` is set on `ion-split-pane` and `ion-menu`. Digging into it, it appears that `contentId` sometimes does not work but `content-id` does. Looks to be some sort of race condition, possibly with either our Angular component wrappers or Web Component upgrading.

### Expected Behavior

I would expect no error/warning to be logged when using contentId as directed.

### Steps to Reproduce

1. Run `ionic start foo sidemenu --type=angular`
2. Run `cd ./foo`
3. Run `ng test`
4. Observe that an error/warning is logged. Since this is a race condition, you may need to run this a few times.

### Code Reproduction URL

_No response_

### Ionic Info

_No response_

### Additional Information

_No response_

Start by generating the Angular sidemenu app with `ionic start foo sidemenu --type=angular`, then run `ng test` repeatedly to reproduce the intermittent warnings. Inspect the Angular component wrappers and Web Component upgrading around `contentId` and `content-id`. Done means the menu and split pane no longer warn when `contentId` is configured.

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