Fix missing padding in custody report dropdown

What does this MR do?

In gitlab-ui!1848 (merged) the padding for dropdown forms was removed, this MR manually adds in the padding to the custody report dropdown which was recently added in !46994 (merged).

Screenshots (strongly suggested)

Before	After

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• [-] Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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