Skip calling promisify on ignore-walk

[LinusU]

(node:17965) [DEP0174] DeprecationWarning: Calling promisify on a function that returns a Promise is likely a mistake.
    at node:internal/util:456:17
    at new Promise (<anonymous>)
    at walk (node:internal/util:441:12)
    at generateDockerignore (file:///Users/linus/coding/loco/api/node_modules/gitignore-to-dockerignore/index.js:25:26)

walk already returns a promise:

https://github.com/npm/ignore-walk/blob/fd253609d86312ecbcafcd16353f5d2bb6e4e7f8/lib/index.js#L298-L303