ci: Set LC_ALL=C to allow running the s390x tests in qemu

Without the fix, the tests immediately abort:

terminate called after throwing an instance of 'std::runtime_error'
  what():  locale::facet::_S_create_c_locale name not valid
./qt/test/test_bitcoin-qt: line 2: 116150 Aborted

ci/test/00_setup_env_s390x.sh

@@ -20,6 +20,7 @@ fi
 export CONTAINER_NAME=ci_s390x
 export DOCKER_NAME_TAG="debian:buster"
 export RUN_UNIT_TESTS=true
+export TEST_RUNNER_ENV="LC_ALL=C"
 export RUN_FUNCTIONAL_TESTS=true
 export GOAL="install"
 export BITCOIN_CONFIG="--enable-reduce-exports --with-incompatible-bdb --with-boost-process"