[FixaMinGata] Add minor margin change

[jonkri]

Please check the following:

• Has the code POD documentation been added or updated?
• Whether this PR should include changes to any public documentation, or the FAQ;
• All cobrand-specific commits start their commit message with the cobrand in square brackets;
• Is new functionality tested? CodeCov will warn you about the diff coverage, but won’t complain about e.g. new files;
• Will cobrand-specific changes require additional work to ensure consistent behaviour on www.fixmystreet.com?
• Are the changes tested for accessibility?
• Have you updated the changelog? If this is not necessary, put square brackets around this: [skip changelog]

See #5050 (comment).