test: use symlinks to copy shells

Git for Windows includes `C:\Program Files\Git\bin\bash.exe`,
which spawns ..\usr\bin\bash.exe, so copying that executable
won't work.

However, if a symlink is used to test paths with spaces,
this executable will still work.

PR-URL: https://github.com/nodejs/node/pull/32129


Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>