Fix flaky test tests/test_microvm_agent_launch.py::test_an_agent_launch_lays_the_bundle_and_inputs_into_the_share_and_runs_the_supervisor

The merge lane saw `tests/test_microvm_agent_launch.py::test_an_agent_launch_lays_the_bundle_and_inputs_into_the_share_and_runs_the_supervisor` fail and then pass on a rerun of the same tree. - Test: `tests/test_microvm_agent_launch.py::test_an_agent_launch_lays_the_bundle_and_inputs_into_the_share_and_runs_the_supervisor` - Tree: `7a1132b60aea71e94fa3813c33b48a67094e30e0` - Lane task: 9850 - Flake record: 01a17274-442b-734e-bbac-f34a5c822b1e Make it deterministic; do not delete it unless it tests nothing.

Flake fixed: fixture bundle_bytes stamped gzip mtime=time(), so two builds a second apart had different sha256 → bundle_corrupt. Pinned mtime=0. Quick gate + container suite green; PR #6844 queued in lane. Memory: none applied.