tests: use assert instead of plain abort.

tests: use assert instead of plain abort.

* tests/actions.at, tests/calc.at, tests/conflicts.at,
* tests/cxx-type.at, tests/glr-regression.at, tests/input.at,
* tests/named-refs.at, tests/regression.at, tests/torture.at,
* tests/local.at:
Prefer assert to abort.