ci: add unity-test-runner/unity-activate as sync-secrets.yml targets

Both thin-wrapper repos' own secrets only ever had UNITY_LICENSE
configured, never the working UNITY_SERIAL/EMAIL/PASSWORD this repo
uses successfully on Windows - this workflow could already sync them
to another repo, but neither was ever a valid target_repo option, so
it was simply never run for them.

Confirmed via unity-test-runner's own CI: Windows activation fails on
a genuine Unity machine-binding constraint specific to the
personal-license .ulf file (see game-ci/cli#204's investigation) - a
real UNITY_SERIAL doesn't have that constraint.

.github/workflows/sync-secrets.yml

@@ -11,6 +11,8 @@ on:
         options:
           - game-ci/orchestrator
           - game-ci/cli
+          - game-ci/unity-test-runner
+          - game-ci/unity-activate
       dry_run:
         description: 'Dry run (list secrets to sync without writing)'
         required: false