Don't log environment variables if debugging isn't enabled (#676)

If debugging _isn't_ enabled, the command evaluated to `set` and just
[printed all the
variables](https://github.com/hazelcast/hazelcast-code-samples/actions/runs/11782852379/job/32818798295)
which was useless.

Author: JackPGreen

.github/workflows/builder.yaml

@@ -16,7 +16,7 @@ jobs:
           distribution: temurin
       - name: Build and test
         run: |
-          set ${RUNNER_DEBUG:+-x}
+          ${RUNNER_DEBUG:+set -x}
           mvn \
             --batch-mode \
             --errors \