bench test asserts a moc error message that newer moc no longer emits

[Kamirus]

cli/tests/bench.test.ts:23 ("rejects moc args with embedded spaces") asserts stderr matches /invalid warning code/. With a newer moc the run still fails as intended, but moc prints its --help output instead of that message, so the assertion fails.

CI pins moc 0.14.13 and passes, so this only shows up locally — it is the one failing test on main on a dev machine, which makes it easy to mistake for damage from whatever you are working on.

Either assert the exit code and a version-agnostic fragment, or pin the moc version for that test case.

[Kamirus]

The test-only workaround (#663) was closed in favor of fixing the root cause: mops bench ignores [toolchain] moc and uses the dfx-bundled compiler (#665). Once bench resolves moc through the toolchain like test/build/check do, the fixture's existing moc = "1.3.0" pin applies locally too and this test is deterministic — that PR should carry Closes #656.