fix: add missing json import in conftest (needed by tiny_conversations_path)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Signed-off-by: Chenhan Yu <chenhany@nvidia.com>

Author: ChenhanYu

tests/examples/speculative_decoding/conftest.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import json
 from pathlib import Path
 
 import pytest