CI does not run on stacked PRs (pull_request trigger restricted to main)

[nazarhussain]

Context

Noted while reviewing #56, which targets the fix/napi-out-parameters-v2 branch (stacked on #57). No CI checks ran on it because .github/workflows/ci.yml triggers only on:

on:
  pull_request:
    branches: [main]

Any PR whose base is another feature branch gets zero checks (build, zig tests, JS tests, lint), so stacked PRs can only be validated locally until the base PR merges or the PR is retargeted.

Proposal

Drop the branch filter on the pull_request trigger (or widen it) so CI runs for PRs against any base branch:

on:
  pull_request:
  push:
    branches: [main]

Ref: .github/workflows/ci.yml

[wemeetagain]

yes this matches what we do in other repos