CI: don't run race-detector on tests with previous Go version

The purpose of running with a previous Go version is to spot usage of
new language features; we don't need to intensively look for bugs.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

.github/workflows/ci.yml

@@ -45,7 +45,8 @@ jobs:
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11 # v4.1.1
       - run: make build
-      - run: make test GO_ONLY=1
+      # Don't run NPM build; don't run race-detector.
+      - run: make test GO_ONLY=1 test-flags=""
 
   test_ui:
     name: UI tests