chore: Do not format boxes with global format (#2326)

`boxes` is using a custom prettier config since it includes frontend
code, so when running `yarn format` at the root of the yarn-project, a
different formatting is applied. This PR omits boxes from the global
yarn format to avoid inconsistencies.

yarn-project/.prettierignore

@@ -2,4 +2,5 @@
 node_modules/
 dest/
 noir-contracts/**/*.json
+boxes/
 *.md