Set kwin_wayland capabilities on install since it needs to be done as root (FS#59988)

PKGBUILD

@@ -4,7 +4,7 @@
 
 pkgname=kwin
 pkgver=5.13.5
-pkgrel=1
+pkgrel=2
 pkgdesc='An easy to use, but flexible, composited Window Manager'
 arch=(x86_64)
 url='https://www.kde.org/workspaces/plasmadesktop/'
@@ -14,6 +14,7 @@ makedepends=(extra-cmake-modules qt5-tools kdoctools)
 optdepends=('qt5-virtualkeyboard: virtual keyboard support for kwin-wayland')
 groups=(plasma)
 source=("https://download.kde.org/stable/plasma/$pkgver/$pkgname-$pkgver.tar.xz"{,.sig})
+install=$pkgname.install
 sha256sums=('d53d380dab763827e4f3effcb4f0725aaec91ded6f702e0fcc5d856829bba151'
             'SKIP')
 validpgpkeys=('2D1D5B0588357787DE9EE225EC94D18F7F05997E'  # Jonathan Riddell

kwin.install

@@ -0,0 +1,9 @@
+post_install() {
+# this is executed by make install, but doesn't work since setcap can only be run as root
+  setcap CAP_SYS_NICE=+ep /usr/bin/kwin_wayland
+}
+
+post_upgrade() {
+  post_install
+}
+