chore: test for describe.only without only failure (#34590)

Adds a regression spec for `node:test` `describe.only()` to ensure it
runs successfully without Deno reporting `Test failed because the "only"
option was used`.

The current node:test implementation already registers top-level
node:test entries with `sanitizeOnly: false`; this locks the issue repro
into the spec suite.

Closes denoland/orchid#342
Closes https://github.com/denoland/deno/issues/31862

Verification:
- `/home/orchid/orch-work/issue-342/target/debug/deno test
describe_only.test.js`
- `cargo test -p specs_tests --test specs node_test_describe_only`

Co-authored-by: divybot <divybot@users.noreply.github.com>
Co-authored-by: Divy Srivastava <me@littledivy.com>