[ROCm][CI/Build] Fix the pytest hook to properly print out the summary (#38585)

Signed-off-by: Gregory Shtrasberg <Gregory.Shtrasberg@amd.com>

docker/Dockerfile.rocm

@@ -390,7 +390,20 @@ ENV MIOPEN_DEBUG_CONV_GEMM=0
 RUN mkdir src && mv vllm src/vllm
 
 # This is a workaround to ensure pytest exits with the correct status code in CI tests.
-RUN echo "import os\n\ndef pytest_sessionfinish(session, exitstatus):\n    os._exit(int(exitstatus))" > /vllm-workspace/conftest.py
+RUN cat << 'EOF' > /vllm-workspace/conftest.py
+import os
+
+_exit_code = 1
+
+def pytest_sessionfinish(session, exitstatus):
+    global _exit_code
+    _exit_code = int(exitstatus)
+
+def pytest_unconfigure(config):
+    sys.stdout.flush()
+    sys.stderr.flush()
+    os._exit(_exit_code)
+EOF
 
 # -----------------------
 # Final vLLM image