Fix red develop c7b0ce8d4562

The merge lane found `develop` red at `c7b0ce8d4562d0ad015b4b07fe2f4cbd3e779537` on its own: no queued PR merges until it is fixed. Failing (tests and gate stages): - `tests/test_plan_matrix.py::test_each_plan_reads_the_matrix[business-trial]` - `api-unit-dc-test` The whole gate log: artifact `7902` on lane task 8717. Make `develop` pass its full gate again. Open a PR as usual: the merge lane merges a PR that fixes some of these and adds no failure even while `develop` is red.

Fixed red develop: tests/billing reset_billing left business-trial's Max agents NULL (missed revision 202610210100's copy), polluting test_plan_matrix on the same worker. Quick gate green; PR #6531 queued to the merge lane.