Set FORCE_PKG_REGISTER=1 when installing packages to avoid failures

when re-using build chroot(8) environments.

This is based on the patch in the PR referenced below, but instead
of using 'reinstall' in two locations (one of which already uses
FORCE_PKG_REGISTER=1), changes the non-embedded behavior.

PR:		205998
Submitted by:	ngie
MFC after:	5 days
Sponsored by:	The FreeBSD Foundation

release/release.sh

@@ -275,6 +275,7 @@ extra_chroot_setup() {
 			PBUILD_FLAGS="${PBUILD_FLAGS} OSREL=${REVISION}"
 			chroot ${CHROOTDIR} make -C /usr/ports/textproc/docproj \
 				${PBUILD_FLAGS} OPTIONS_UNSET="FOP IGOR" \
+				FORCE_PKG_REGISTER=1 \
 				install clean distclean
 		fi
 	fi