Only add the correct type to new signatures to avoid breaking the hash
of old ones.

(cherry picked from commit 8a9d8238)

Conflicts:
	xmlsecurity/qa/unit/signing/signing.cxx

Change-Id: I30f892b292f84a0575a3d4ef5ccf3eddbe0090ca
Reviewed-on: https://gerrit.libreoffice.org/70451
Tested-by: Jenkins
Tested-by: Xisco Faulí <xiscofauli@libreoffice.org>
Reviewed-by: Michael Stahl <Michael.Stahl@cib.de>