[ci] Test pytest-forked boxing

This wraps all tests in pytest-forked so that segfaults and other
process-terminations are properly reported by pytest

TODO: Evaluate runtime overhead

Author: driazati

tests/scripts/setup-pytest-env.sh

@@ -63,6 +63,10 @@ function run_pytest() {
         extra_args+=('--reruns=3')
     fi
 
+    if [[ ! "${extra_args[@]}" == *" -n"* ]]; then
+        extra_args+=("-n=1")
+    fi
+
     suite_name="${test_suite_name}-${ffi_type}"
     exit_code=0
     TVM_FFI=${ffi_type} python3 -m pytest \