Resolve CodeQL alerts for checked-in .yarn paths in some samples

[jonthysell]

Now that CodeQL is scanning this repo, and even though I'm trying to prevent scanning the samples (as they're non-production) we're getting issues thanks to the checked-in yarn binaries in the .yarn folders of several samples and the security issues they bring with them.

It's hard to tell if we can remove the folders entirely (see yarnpkg/yarn#7741) or if we'll have to try to exclude them from CodeQL scanning.