ci(audience): write Unity activation log to /tmp so it stays out of CI artifacts (SDK-317)

- The Linux PlayMode container script teed Unity license activation output to
  /github/workspace/artifacts/activation.log, and the workflow uploads everything under
  that directory as a downloadable artifact.
- Unity's activation log can include sensitive account or entitlement details, so anyone
  with read access to the workflow run could pull them out of the artifact zip.
- Moves ACTIVATION_LOG to /tmp/audience-unity-activation.log. The two grep checks that gate
  success / failure still read the same file, just from /tmp, and the file never reaches
  the artifact upload.

Linear: SDK-317

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: ImmutableJeffrey

.github/scripts/audience/playmode-linux-container.sh

@@ -6,7 +6,7 @@
 set -uo pipefail
 
 LOG=/github/workspace/artifacts/unity.log
-ACTIVATION_LOG=/github/workspace/artifacts/activation.log
+ACTIVATION_LOG=/tmp/audience-unity-activation.log
 RESULTS=/github/workspace/artifacts/test-results.xml
 PROJECT=/github/workspace/examples/audience