linux-pine64-pinetab2: use $pkgver in $_tags (MR 5299)

This is usually how it's done so you only need to change the pkgver in
one place.

device/testing/linux-pine64-pinetab2/APKBUILD

@@ -27,7 +27,7 @@ makedepends="
 "
 
 # Source
-_tags="v6.9.3-danctnix1"
+_tags="v$pkgver-danctnix1"
 _config="config-$_flavor.$arch"
 source="
 	$pkgname-$_tags.tar.gz::https://github.com/dreemurrs-embedded/linux-pinetab2/archive/$_tags.tar.gz