tests: Fixed steroids test case
tests: Fixed steroids test case

Use g_assert_error() and g_assert_cmpstr() instead in places and also
fix where the asserts were failing. In this case, it was failing in
cancel callbacks where we asserted the error was NULL and then tried
to free it after.

hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,hoheinzollern/tracker,outofbits/tracker,outofbits/tracker,outofbits/tracker,hoheinzollern/tracker,hoheinzollern/tracker,outofbits/tracker