chore(artifact): keep runtime dependency fix minimal

Remove the packed-package test, CI step, and related documentation.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

CONTRIBUTIONS.md

@@ -29,13 +29,6 @@ To run unit tests for the `@actions/artifact` package:
 3. Change working directory to `packages/artifact`
 4. Run jest tests: `npm run test`
 
-After building the package, run `npm run test:package` from `packages/artifact`
-to pack it, install it in a temporary consumer with only production dependencies,
-and check that its public entry point and protobuf RPC runtime can be imported.
-This check requires access to the npm registry and also runs in the unit-test CI
-matrix, without monorepo hoisting or code-generation tooling masking missing
-runtime dependencies.
-
 ## Within upload-artifact or download-artifact actions
 
 Any easy way to test changes for the official upload/download actions is to fork them, compile changes and run them.