test: check the finalizer error inside FinalizerError, not its message

[lesnik512]

Two tests fail against modern-di 4.1.0:

• tests/test_aio.py::test_wrap_unary_aio_resets_context_var_when_close_raises
• tests/test_inject.py::test_wrap_unary_sync_resets_context_var_when_close_raises

Both used pytest.raises(RuntimeError, match="boom"). "boom" is the message of the finalizer's own exception, and on 4.0.0 FinalizerError's message included it. In 4.1.0 (modern-python/modern-di#631) the message is a summary, Container.close_sync() found 1 finalizer error(s): RuntimeError (1), so the match fails. The integration code is unaffected.

The tests now catch FinalizerError and check that its only exception is RuntimeError("boom"). That checks the same thing without depending on the message text. They still go on to check that the context variable was reset, which is what they are for.

Tests

• The two tests failed on 4.1.0 before this change.
• With the change, all 30 tests pass on 4.1.0 and on 4.0.0, so the modern-di>=4,<5 range stays covered.
• just lint and just test-ci (100% coverage) pass.