test: add required flag to FinalizationGroupError test
Related: https://github.com/nodejs/node-v8/issues/156#issuecomment-617482518
Note: this is target to canary-base
Checklist
-
make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines