Skip empty SYCL device selector in CI

Author: allnes

.github/workflows/sycl-ci.yml

@@ -67,7 +67,12 @@ jobs:
       run: cmake --build build --parallel
 
     - name: Test
-      run: ONEAPI_DEVICE_SELECTOR="${DEVICE_SELECTOR}" ctest --test-dir build --output-on-failure --parallel
+      run: |
+        if [ -n "${DEVICE_SELECTOR}" ]; then
+          ONEAPI_DEVICE_SELECTOR="${DEVICE_SELECTOR}" ctest --test-dir build --output-on-failure --parallel
+        else
+          ctest --test-dir build --output-on-failure --parallel
+        fi
 
   build-sycl-adaptivecpp-arm64:
     name: ${{ matrix.platform }} / ${{ matrix.build_type }}