Fix CI

[mmore500]

from @claude

The coverage job installs lcov from Ubuntu's apt repo. When that package upgraded to lcov 2.0, one of its headline changes was "improved error checking and error management" — including promoting line-number mismatches to fatal errors. Under lcov 1.x these were silent or warnings, so identical source/CI configs that passed for months suddenly hard-fail. The mismatch report itself even points at the new flag: "use geninfo --ignore-errors mismatch ... to bypass this error."

In our case geninfo flags PyInit_systematics at systematics_bindings.cpp:180 (declared end line 180, observed end line 841). That gap is just pybind11's PYBIND11_MODULE macro expanding into a much larger function body — nothing in the bindings is actually wrong. The fix is to pass --ignore-errors mismatch to the lcov --capture step. Background discussion: linux-test-project/lcov#209 and #341.