Let the GPU verify caller turn on the memory probe (#48001)

transformers-ci#75 added a `memory_probe` input to the reusable
serge-verify-slow workflow: it installs the resource plugin, sets
PYTEST_RESOURCE_METRICS_FILE / PYTEST_RESOURCE_GC_PROBE and uploads a
per-test JSONL saying how much device memory each test leaves behind and
how much of that survives a gc.collect(). This caller is the only
dispatchable entry point, so without the passthrough the input is
unreachable.

Off by default, and the reusable workflow reads an empty string as off,
so serge's normal dispatches are unchanged. It stays opt-in on purpose:
the probe's collect frees memory and can stop a memory-related failure
from reproducing.