parse: fix missing occurrence of ${VERSION_SEPARATOR}

In case of ${STABLE}, the version line comes from a previous utag, which
means it was written by umpf itself using ${VERSION_SEPARATOR}, which
was previously hard-coded as "-". Use it also when parsing back the
version.

Fixes: a864fe6 (2023-04-20, "umpf: split off VERSION_SEPARATOR from VERSION")

umpf

@@ -928,7 +928,7 @@ parse() {
 		test -n "${content}" || bailout "${cmd} line without value"
 		if ${STABLE}; then
 			local name="$(<"${STATE}/name")"
-			local version="$(sed "s;${name}/\([0-9]\{8\}\)-.*;\1${VERSION_SEPARATOR}${VERSION};" <<< "${content}")"
+			local version="$(sed "s;${name}/\([0-9]\{8\}\)${VERSION_SEPARATOR}.*;\1${VERSION_SEPARATOR}${VERSION};" <<< "${content}")"
 			local tagname="${name}/${version}"
 			echo "${version}" > "${STATE}/version"
 			echo "${tagname}" > "${STATE}/tag"