testing/avarice: add linux-headers to makedepends

testing/avarice/APKBUILD

 # Maintainer: Marian Buschsieweke <marian.buschsieweke@posteo.net>
 pkgname=avarice
 pkgver=2.14
-pkgrel=3
+pkgrel=4
 pkgdesc="AVaRICE interfaces with GDB and allows debugging of AVR MCUs"
 url="https://github.com/avrdudes/avarice"
 arch="all"
@@ -13,6 +13,7 @@ makedepends="
 	hidapi-dev
 	libusb-compat-dev
 	libusb-dev
+	linux-headers
 	perl
 	"
 depends="gdb-multiarch"