test(testkit): await alias resolver rejection

[Anber]

Motivation

The aliased-specifier test starts an asynchronous rejection assertion but finishes before the assertion settles. afterEach can then dispose its evaluation broker while the transform is still running. With terminal broker disposal, this produces Eval broker has been disposed instead of the expected missing-module error, which Jest can attribute to the following resolver test.

Await the assertion so the expected rejection completes before cleanup starts.

Test plan

• pnpm run prepare: 16 build tasks passed.
• pnpm check:all: 32 tasks passed, including tests and type checks; ESLint and dependency consistency checks passed. Testkit: 150 tests and 279 snapshots passed, 2 tests skipped.
• Controlled runs against WyW before and after terminal broker disposal confirmed the race: the original assertion left a runner alive before the change and failed after it; adding await passed and exited normally in all three repeated runs on each revision.

This only changes a test in the private testkit package; no release changeset is needed.

[changeset-bot]

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Latest commit: ceb40db

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