test: include agy in OPTIONAL_EXECUTION_PROVIDERS assertion (hotfix #217 CI break)

[LeoLin990405]

Summary

Hotfix for the CI breakage on main after #217 merged. One test
expected the old OPTIONAL_EXECUTION_PROVIDERS set; #217 added agy
to OPTIONAL_PROVIDER_NAMES (which the execution registry aliases),
so the test needs to be updated.

Broken CI run (8/11 jobs failed, all with the same single
failure):
https://github.com/SeemSeam/claude_codex_bridge/actions/runs/26735236338

test/test_v2_execution_registry.py:13: in test_execution_registry_can_build_core_only_registry
    assert set(OPTIONAL_EXECUTION_PROVIDERS) == {'opencode', 'droid'}
E   AssertionError: assert {'agy', 'droid', 'opencode'} == {'droid', 'opencode'}
========== 1 failed, 2239 passed, 21 deselected in 1279.87s ==========

Fix

lib/provider_execution/registry.py:12:

OPTIONAL_EXECUTION_PROVIDERS = OPTIONAL_PROVIDER_NAMES

Pure alias — so the expected set must follow OPTIONAL_PROVIDER_NAMES
literally. Updates the assertion to {'opencode', 'droid', 'agy'} and
adds assert registry.get('agy') is None to maintain coverage
parity with opencode/droid in the include_optional=False path
(since agy has execution_adapter=None in #217 anyway).

My mistake

I tested 12 agy-related test cases locally before opening #217 but
didn't run the full suite, so this test slipped through. PR #211
(the precursor I rebased) also did not catch it because they only ran
the 6 files listed in their PR description.

After this hotfix lands, the recommended verification command
becomes:

uvx --with pyyaml --with tomli pytest \
  test/test_v2_provider_catalog.py \
  test/test_v2_provider_core_registry.py \
  test/test_v2_execution_registry.py \
  test/test_v2_runtime_launch.py -q

Sorry for the breakage @SeemSeam — apologies for not catching this
in #217. 🙏

[SeemSeam]

ok I just commit and still not use in the release before test