Incorrect error highlighting in syntax/PKGBUILD.vim

From James Harvey (jamespharvey20) via https://bugs.archlinux.org/task/61923:

"vimfiles/syntax/PKGBUILD.vim" highlights two things as errors that it should not. As an example, the valid official PKGBUILD file for gdb: https://git.archlinux.org/svntogit/packages.git/plain/trunk/PKGBUILD?h=packages/gdb

pkgname=(gdb gdb-common) ... sha1sums=(... 'SKIP')

It highlights in: "pkgname" the '(', ' ', and ')'; and "sha1sums" the "SKIP".

"pkgname" can of course be an array for split packages.

Any of "md5sums", "sha1sums", "sha224sums", "sha256sums", "sha384sums", and "sha512sums" can of course contain "SKIP".

Even though the error highlighting is technically wrong, maybe it's desired to be left as-is to discourage "pkgname" being a single element array or "SKIP" usage when inappropriate, etc.

On the mailing list, Morten Linderud pointed out that without pacman-contrib's vim PKGBUILD files, vim aliases PKGBUILD's to filetype bash, which doesn't highlight improper errors. Perhaps pacman-contrib's vim PKGBUILD files could be considered for removal. I personally like the idea of having the stricter highlighting that pacman-contrib provides. Seeing top variables as the same color as functions for a PKGBUILD just feels weird after all this time, too. https://lists.archlinux.org/pipermail/arch-general/2019-March/046195.html

There might of course be other valid PKGBUILD scenarios pacman-contrib's files don't handle, these are just the 2 I see a lot.

Additional info:

pacman-contrib 1.1.0-1

Steps to reproduce:

$ vim