fix #39010 - add left margin to 1st time contributor badge

What does this MR do?

Added 4px margin-left to 1st time contributor badge.
Element attribute selector preferred under .issuable-meta class for specificity.

Before

After

What are the relevant issue numbers?

#39010 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated via this MR
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Tested in all supported browsers
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #39010 (closed)