fix(Makefile): defensively validate scoop output path

[xudyang1]

scoop prefix package on Git Bash returns 0 and writes error to stdout even if scoop does not find the package. (ScoopInstaller/Scoop#6228)

Both #1252 and this change will work if future scoop returns 1 for unknown package

---

#1252 will fail when the followings happen:

1. scoop still returns 0 for unknown package AND
2. grep -v 'Could not find app path for' fails by
   2.1. scoop changes error message of scoop prefix package, OR
   2.2. scoop prefix neovim returns a path that contains Could not find app path for (very rare)

The following change enables defensive path validation against the output. Works on either forward slash or backslash as path separator.

-               if (scoop prefix neovim | grep -v 'Could not find app path for') >/dev/null 2>&1; then \
+               if (scoop prefix neovim | grep '^[A-Z]:[/\\]') >/dev/null 2>&1; then \

[L3MON4D3]

Ahh I see, this should be more safe 👍
TY!!