fix(buttons): Correct dropdown button styles for secondary and tertiary categories

What does this MR do?

Dropdown button

category variant	before	after
primary default
secondary default
tertiary default
primary dashed
secondary dashed
tertiary dashed
primary info
secondary info
tertiary info
primary success
secondary success
tertiary success
primary warning
secondary warning
tertiary warning
primary danger
secondary danger
tertiary danger
primary link
secondary link
tertiary link

Dropdown icon button

category variant	before	after
primary default
secondary default
tertiary default
primary dashed
secondary dashed
tertiary dashed
primary info
secondary info
tertiary info
primary success
secondary success
tertiary success
primary warning
secondary warning
tertiary warning
primary danger
secondary danger
tertiary danger
primary link
secondary link
tertiary link

Dropdown split button

category variant	before	after
primary default
secondary default
tertiary default
primary dashed
secondary dashed
tertiary dashed
primary info
secondary info
tertiary info
primary success
secondary success
tertiary success
primary warning
secondary warning
tertiary warning
primary danger
secondary danger
tertiary danger
primary link
secondary link
tertiary link

Dropdown split icon button

category variant	before	after
primary default
secondary default
tertiary default
primary dashed
secondary dashed
tertiary dashed
primary info
secondary info
tertiary info
primary success
secondary success
tertiary success
primary warning
secondary warning
tertiary warning
primary danger
secondary danger
tertiary danger
primary link
secondary link
tertiary link

Does this MR meet the acceptance criteria?

Conformity

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• GitLab UI's contributing guidlines.
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  • GitLab: mr_url
  • Customers Portal: mr_url
  • Status Page: mr_url
• Added the ~"component:*" label(s) if applicable.

Security

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