release.sh: Pass PKGCONF through to make release

Otherwise setting PKGCONF=1 in the release.conf file doesn't actually
result in pkgbase bits being produced and shipped on images.

MFC after:	1 minute
Sponsored by:	https://www.patreon.com/c/cperciva

release/release.sh

@@ -199,7 +199,7 @@ env_check() {
 		KERNCONF=\"${KERNEL}\" ${CONF_FILES} ${SRCPORTS} \
 		WITH_DVD=${WITH_DVD} WITH_VMIMAGES=${WITH_VMIMAGES} \
 		WITH_CLOUDWARE=${WITH_CLOUDWARE} WITH_OCIIMAGES=${WITH_OCIIMAGES} \
-		XZ_THREADS=${XZ_THREADS}"
+		XZ_THREADS=${XZ_THREADS} PKGCONF=${PKGCONF}"
 
 	return 0
 } # env_check()