passthrough-arguments leads to trailing slashes in argument key on Windows

[asimen1]

Description:
Using -P, --passthrough-arguments leads to trailing slashes in argument key on Windows (and stackblitz.com).

On local Mac doesn't reproduce.
If adding only the key without value (e.g. yarn test --key) doesn't reproduce as well.

Expected Behavior:
Argument key should not have a trailing slash when specifying argument value.

Environment:
concurrently v7.6.0
OS: Windows 10
Node v16.14.2

Reproduction:
stackblitz
in terminal type: npm run test -- --key=value or yarn test --key=value

See Images attached:

[gustavohenke]

@paescuj one you might like 😃
I don't remember why exactly we needed shell-quote. It's definitely causing this (it's right here). Was it to support expanding e.g. {@} when already wrapped in quotes?