The issue from yesterday was closed (https://github.com/bitcoin/bitcoin/issues/30601#event-13795338265), so opening a new issue for this, because the workaround does not fix the issue.
The error is:
0test/system_tests.cpp(88): error: in "system_tests/run_command": check what.find(expected) != std::string::npos has failed
As a temporary workaround, one can try --disable-external-signer
, if they don’t need it. Alternatively, they can set a different locale, for just the tests.
A fix would be something like #28286, if someone wants to pick that up.