test: mock-fs does not work as expected for Node >20.4

[stennie]

mock-fs is currently used for test/generator/local.js. Tests pass in Node 20.4 and earlier, but fail in more recent versions of Node.

Possible related to: tschaub/mock-fs#377

Since this is a very limited use case, I think it could be resolved by either:

• creating a sample directory to avoid the need for monkey patching core fs behaviour
• using memfs or an alternative package

[basti1302]

I totally agree. The sample directory sounds like the most straightforward option to me.