only apply the custom code font on actual code input
only apply the custom code font on actual code input

Applying it to none code breaks a lot of UI as GitHub often relays on a set size and code fonts have varying default sizes.

busches/refined-github,sindresorhus/refined-github,jgierer12/refined-github,sindresorhus/refined-github,jgierer12/refined-github,busches/refined-github