Fix some of the tests in `tests::shell` (#12417)

# Description
Some of the tests in `tests::shell` were using `sh` unnecessarily, and
had `#[cfg(not(windows))]` when they should be testable on Windows if
`sh` is not used.

I also found that they were using `.expect()` incorrectly, under the
assumption that that would check their output, when really an
`assert_eq!` on the output is needed to do that. So these tests weren't
even really working properly before.

# User-Facing Changes
None

# Tests + Formatting
- :green_circle: `toolkit fmt`
- :green_circle: `toolkit clippy`
- :green_circle: `toolkit test`
- :green_circle: `toolkit test stdlib`

0 files changed, 0 insertions, 0 deletions