[Testing]: test handleArgsSocketCatchError is called on unlink error

[jsjoeio]

We don't have coverage on L41 in app.ts:

https://github.com/coder/code-server/blob/main/src/node/app.ts#L41

We should be able to test this by:

• exporting listen
• passing in a directory instead of a file for socket

These are the errors that unlink can throw: https://man7.org/linux/man-pages/man2/unlink.2.html#ERRORS