build/github: use --test_summary=terse in unit_tests

After --test_output=summary, bazel still emits its end-of-run summary
roster listing every test target with PASSED/FAILED status. For a CI
job that runs ~900 test targets, that's ~900 lines of PASSED noise
trailing the actual failure line, with each cached target taking a row
like:

  //pkg/build/bazel:bazel_test          (cached) PASSED in 0.1s

--test_summary=terse drops the PASSED rows and keeps only the failed
targets (plus the FLAKY/TIMEOUT categories). The "Executed N out of M"
line stays, so the overall run shape is still visible at a glance.

Release note: None
Epic: none

Author: tbg

build/github/unit-tests.sh

@@ -34,5 +34,5 @@ bazel test $TEST_TARGETS //pkg/ui:lint //pkg/ui:test \
     --config crosslinux --jobs 200 \
     --bes_keywords ci-unit-test --config=use_ci_timeouts \
     --build_event_binary_file=bes.bin $(./build/github/engflow-args.sh) \
-    --test_output=summary --noshow_progress \
+    --test_output=summary --test_summary=terse --noshow_progress \
     $EXTRA_PARAMS