Re-enable cargo-outdated in CI

See kbknapp/cargo-outdated#389. The bug has been
masked by kornelski/cavif-rs@d157737.

Author: dtolnay

.github/workflows/ci.yml

@@ -102,4 +102,3 @@ jobs:
       - uses: dtolnay/install@cargo-outdated
       - run: cargo outdated --exit-code 1
       - run: cargo outdated --workspace --exit-code 1
-        continue-on-error: true  # https://github.com/kbknapp/cargo-outdated/issues/389