[Chore]: Investigate integration test flakes

[jsjoeio]

Description

For some reason, the installExtesion test has been flaking out and we're not sure why:
https://github.com/coder/code-server/runs/7458796120?check_suite_focus=true#step:9:13

Solution

Replace it with another test like --help which fails if used on the wrong platform

For example, running --help with the Linux release on macOS results in this error: