deno: tests run with `--no-check`

`packages/deno/package.json`: `deno test ... --no-check`. Type errors in Deno test files never fail CI. `lint:types` covers `src` only.

Either drop `--no-check`, or add a separate `deno check test/` step. Measure the added CI time first; `--no-check` may have been added for speed.

Start in packages/deno/package.json and inspect the deno test command using --no-check, alongside the lint:types coverage for src. Measure the added CI time for type-checking the test files, then choose whether removing --no-check or adding a separate deno check test/ step meets the goal. Done means Deno test-file type errors can fail CI without an unacceptable time increase.

Written by the indexing model from the issue text.