fix two tests that have failed CI on every run since 2026-08-19

[devdanzin]

CI has been red on main for five consecutive merges — #261, #262, #263, #264, #265 (and
#266, which I merged on top of it). Neither failure is caused by any of those PRs. Both
are tests asserting a property of the interpreter build rather than of fusil, so both pass
on the local interpreters and fail on the python.org builds setup-python installs.

A permanently red CI catches nothing, which is exactly how a real regression gets in.

1. test_builtins_still_discoverable_under_only_c

AssertionError: 'math' not found in {'_tokenize', '_ast', 'sys', 'pwd', ...}

Whether math is compiled in or is a shared extension is a build choice. It is a builtin on
both interpreters here and an extension on CI, so the test was naming a module CI does not
have.

The invariant it actually guards — a builtin has no filename, so routing the seed through the
file-based --only-c check must not drop it — is now asserted over
sys.builtin_module_names, whatever this interpreter happens to contain.

2. test_tricky_objects_runs_without_types_CapsuleType

AssertionError: True is not false     # assertFalse(hasattr(shim, "CapsuleType"))

The test builds a shim types module holding every attribute except CapsuleType, to prove
the generated prelude survives a target that lacks it (PyPy 3.11, CPython < 3.13). It copied
__getattr__ along with everything else — and CPython 3.13 defines CapsuleType lazily
through a module-level __getattr__ (PEP 562), so the copy resolved the attribute straight
back to the real module and the shim stopped shimming.

3.14 defines it eagerly via _types, which is why this passed locally and failed only on the
3.13 job. Skipping __getattr__ fixes it.

No 3.13 is installed here, so I verified the mechanism against a simulated 3.13-style lazy
types rather than claiming a test run I did not do:

under a 3.13-style lazy types, shim hasattr CapsuleType: False

Scope

Tests only — no change to fusil. 1281 tests OK locally, ruff check and
ruff format --check both clean.