ci: Ensure composefs is enabled on Fedora

For some reason we're not picking this up in the Prow build,
which breaks things because now rpm-ostree hard requires it.

Let's make this a fatal build time error for more clear
debugging.

ci/build.sh

@@ -17,7 +17,7 @@ ${dn}/installdeps.sh
 if test "${OS_ID}" = 'fedora'; then
     case "${CONFIGOPTS:-}" in
         *--with-soup*|*--without-curl*) ;;
-        *) CONFIGOPTS="${CONFIGOPTS:-} --with-curl"
+        *) CONFIGOPTS="${CONFIGOPTS:-} --with-curl --with-composefs"
     esac
 fi
 case "${CONFIGOPTS:-}" in