feat(Popover): Use heading scale

What does this MR do?

We are trying to increase results, quality, and efficiency by using typography in a systematic way.

This MR updates popover to use the heading scale implemented in !3673 (merged).

gl-heading-scale-200 is used as the semantic heading scale does not visually align (see contextual adjustments).

This MR also removes a non-compliant <strong> from a story which uses popover. This change does not update the path component.

For more context see:

• Type scale > Implement type scale specs (#2137 - moved)

Not in scope

• There are known accessibility issues with this component #1202 (moved)
• Component uses a h3 which is probably not the right element, there is no clear path forward to change this element so this is out of scope.

Screenshots or screen recordings

Before	After

Integration merge requests

• GitLab: gitlab!132746 (closed)
• CustomersDot: mr_url
• Status Page: mr_url

UI kit follow up

• Figma > Popover - update title/heading styles (gitlab-org/gitlab-services/design.gitlab.com#1708 - closed)

Does this MR meet the acceptance criteria?

This checklist encourages the authors, reviewers, and maintainers of merge requests (MRs) to confirm changes were analyzed for conformity with the project's guidelines, security and accessibility.

Toggle the acceptance checklist

Conformity

• Code review guidelines.
• GitLab UI's contributing guidelines.
• If it changes a Pajamas-compliant component's look & feel, the MR has been reviewed by a UX designer.
• If it changes GitLab UI's documentation guidelines, the MR has been reviewed by a Technical Writer.
• If the MR changes a component's API, integration MR(s) have been opened (see integration merge requests above).
• Added the ~"component:*" label(s) if applicable.

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• Security reports checked/validated by a reviewer from the AppSec team

Accessibility

If this MR adds or modifies a component, take a few moments to review the following:

• All actions and functionality can be done with a keyboard.
• Links, buttons, and controls have a visible focus state.
• All content is presented in text or with a text equivalent. For example, alt text for SVG, or aria-label for icons that have meaning or perform actions.
• Changes in a component’s state are announced by a screen reader. For example, changing aria-expanded="false" to aria-expanded="true" when an accordion is expanded.
• Color combinations have sufficient contrast.