Mention that pull requests cannot use issue forms

[Calinou]

Why:

Closes #8701

What's being changed:

Add a mention that pull requests cannot use issue forms, but only traditional pull request templates. (Correct me if I'm wrong 🙂)

Check off the following:

• I have reviewed my changes in staging (look for the latest deployment event in your pull request's timeline, then click View deployment).
• For content changes, I have completed the self-review checklist.

Writer impact (This section is for GitHub staff members only):

• This pull request impacts the contribution experience
  • I have added the 'writer impact' label
  • I have added a description and/or a video demo of the changes below (e.g. a "before and after video")

[welcome]

Thanks for opening this pull request! A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[ajs256]

I would put it above the "This example..." paragraph because it looks a little weird as it is:

Also, the note should be in a callout box:

{% note %}
**Note:** Take notes!
{% endnote %}

Maybe also link to the article about PR templates (/communities/using-templates-to-encourage-useful-issues-and-pull-requests/creating-a-pull-request-template-for-your-repository). Not sure if that's necessary though.

[ramyaparimi]

@Calinou Thanks so much for opening a PR! I'll get this triaged for review ⚡

[ethanpalm]

👋🏼 @Calinou, thanks for creating this PR! I think this information can definitely help people who might try to use issue forms with pull requests. I've made just a few minor changes to align the content with our style guide. I'm going to update the branch and will get this merged as soon as all the checks are passing.

Thanks for contributing to the GitHub docs! ⚡

[ethanpalm]

Good catch on the spacing here 😁

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