Better error messages for unit tests

Previously it always said "syntax error", even when there was some
other kind of exception thrown, or the test file simply returned a
false value.

Now those two cases are distinguished, and in case of an actual syntax
error, the string "syntax error" is already in $@
Fixed: DynamicField configuration in SysConfig 'DefaultOverviewColumns' causes JS error (bug#10397).

Conflicts:
	CHANGES.md
Fixed bug#10400 - AgentTicketProccess will not use error messages of dynamic field drivers.
Fixed: Dynamic field not visible in queue view screen (AgentTicketOverviewSmall.dtl) (bug#10340).
Merge remote-tracking branch 'upstream/master' into otrs-master