DF031 false positive for `pnpm install --frozen-lockfile`

[dkalinkov]

When running droast over Dockerfile containing:

RUN pnpm install --frozen-lockfile

droast incorrectly flags:

   INFO  [DF031]  npm install used — consider npm ci for reproducible builds
             at Dockerfile:10
             💬 "`npm install` in a Dockerfile: non-deterministic, slower than `npm ci`, and potentially installs different versions than your lockfile specifies. `npm ci` exists specifically for CI/CD and containers. Use it."

[dkalinkov]

i guess its because of the simple check here -> https://github.com/immanuwell/dockerfile-roast/blob/main/src/rules.rs#L443

will create a pr when i have more time.