eosio_bios_if_tests/set_1_finalizer fails under default Savanna libtester

[linh2931]

tests/eosio.bios_inst_fin_tests.cpp(60): error: in "eosio_bios_if_tests/set_1_finalizer": check output_json.find("\"generation\": 1") != std::string::npos has failed [18446744073709551615 == 18446744073709551615]
tests/eosio.bios_inst_fin_tests.cpp(91): error: in "eosio_bios_if_tests/set_2_finalizers": check output_json.find("\"generation\": 1") != std::string::npos has failed [18446744073709551615 == 18446744073709551615]

We need to start with legacy_tester as the test transitions to Savanna explicitly by calling setfinalizers host function:

reference-contracts/tests/eosio.bios_inst_fin_tests.cpp

Line 19 in cd645b5

class eosio_bios_if_tester : public tester {