chore: restore followsDesignSystem flag for toggle & loading icon

What does this MR do?

!1280 (merged) removed followsDesignSystem flag from multiple components due to fixes to our visual integration job In !1300 (merged) our original intent was to restore flags for all components which actually are ok, but these two slipped throught.

This MR fixes this

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines.
• GitLab UI's contributing guidlines.
• 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 in the following projects to ensure that the @gitlab/ui package can be upgraded quickly after the changes are released:
  • GitLab: mr_url
  • Customers Portal: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.