fix(ci): correct test artifact paths in unity-tests workflow (#561)

- Explicitly set artifactsPath for game-ci/unity-test-runner
- Fix upload paths to match where artifacts are actually created
- Add if-no-files-found: warn to prevent failures on missing artifacts

The test runner outputs to repo root artifacts/ folder, not inside
the project directory.

Signed-off-by: JasonXuDeveloper - 傑 <jason@xgamedev.net>
Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

Author: JasonXuDeveloper

.github/workflows/unity-tests.yml

@@ -60,6 +60,7 @@ jobs:
           projectPath: ${{ inputs.project_path }}
           unityVersion: ${{ inputs.unity_version }}
           testMode: EditMode
+          artifactsPath: artifacts/EditMode
           githubToken: ${{ secrets.GITHUB_TOKEN }}
           checkName: EditMode Test Results
 
@@ -76,6 +77,7 @@ jobs:
           projectPath: ${{ inputs.project_path }}
           unityVersion: ${{ inputs.unity_version }}
           testMode: PlayMode
+          artifactsPath: artifacts/PlayMode
           githubToken: ${{ secrets.GITHUB_TOKEN }}
           checkName: PlayMode Test Results
 
@@ -85,15 +87,17 @@ jobs:
         uses: actions/upload-artifact@v4
         with:
           name: EditMode-results-${{ inputs.unity_version }}
-          path: ${{ inputs.project_path }}/artifacts/EditMode
+          path: artifacts/EditMode
+          if-no-files-found: warn
           retention-days: 14
 
       - name: Upload PlayMode test results
         if: always() && (inputs.test_mode == 'All' || inputs.test_mode == 'PlayMode')
         uses: actions/upload-artifact@v4
         with:
           name: PlayMode-results-${{ inputs.unity_version }}
-          path: ${{ inputs.project_path }}/artifacts/PlayMode
+          path: artifacts/PlayMode
+          if-no-files-found: warn
           retention-days: 14
 
       # Generate test summary