Fix lint CI: install from lockfile (npm ci) instead of lockless yarn (#365)

The lint job ran `yarn` with no `yarn.lock` in the repo, so yarn ignored
package-lock.json and resolved every dependency fresh from the
package.json ranges. prettier isn't a direct dependency — it comes in
transitively via gts (^3.6.2) — so CI floated to the newest prettier
(3.9.4), while local development pins 3.8.1 through package-lock.json.

prettier 3.9.x changed how it wraps union return types (collapsing the
leading-`|` multiline form 3.8.1 produces), so `gts check` failed in CI
on heap-profiler.ts / heap-profiler-bindings.ts even though the code was
correctly formatted for the pinned prettier — and the failure never
reproduced locally.

Switch install to `npm ci` (and the script to `npm run lint`) so CI uses
the exact package-lock.json versions the repo is developed against. This
fixes the prettier drift and prevents any future lockless-yarn float for
every other tool in the lint chain.

Author: szegedi

.github/workflows/lint.yml

@@ -10,5 +10,5 @@ jobs:
     steps:
       - uses: actions/checkout@v7
       - uses: actions/setup-node@v6
-      - run: yarn
-      - run: yarn lint
+      - run: npm ci
+      - run: npm run lint