test: Makefile.am: add missing exception dependency
test: Makefile.am: add missing exception dependency

The read header includes references to the SdBusError object
but doesn't link against anything providing it.

Change-Id: Id3e9f88557c1b4eeaedd095cb50515f08055e685
Signed-off-by: Patrick Venture <36c53fa43f47f3fd67cb2fc38031827244d18a1f@google.com>

openbmc/sdbusplus,openbmc/sdbusplus,openbmc/sdbusplus,openbmc/sdbusplus