CI: only run on PRs targeting main (skip develop)

[jakobklippel]

Summary

The CI workflow currently runs on PRs targeting both develop and main. We want it to run only on PRs from develop → main, not on PRs into develop. This cuts noise and CI minutes on the day-to-day branch flow while keeping the gate where it actually matters (release into main).

Change

In .github/workflows/ci.yml, narrow the pull_request trigger from:

on:
  pull_request:
    branches: [develop, main]
  workflow_dispatch:

to:

on:
  pull_request:
    branches: [main]
  workflow_dispatch:

workflow_dispatch stays so the workflow can still be triggered manually on any branch when needed.

Verify

• Open a test PR into develop → CI should NOT run.
• Open a test PR from develop into main → CI SHOULD run.
• Trigger via the Actions UI on an arbitrary branch → still runs.

Affected files

• loopstack/.github/workflows/ci.yml

Out of scope

• release.yml and release-studio-docker.yml — not touched, those have their own triggers (tags / manual).
• Branch protection rules on develop may currently require this CI check; if so, that requirement needs to be removed in the GitHub repo settings as part of this change.

[jakobklippel]

Linked to PR #205: #205