phosphor-user-manager: srcrev bump 3ab6cc280e..fdf0937353

Patrick Williams (2):
      sdbusplus: remove deprecated variant_ns
      sdbusplus: replace message::variant with std::variant

(From meta-phosphor rev: ced0054c3669c95147f17bbbadca185b7a0af375)

Change-Id: Ie36f4fda742944dfa32d873370921e5dea2dfaa1
Signed-off-by: Andrew Geissler <openbmcbump-github@yahoo.com>
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>