Optimize GitHub Actions: Prevent duplicate workflow runs on PRs

Currently, workflows trigger twice for pull requests:
1. Once via 'push' event when pushing to PR branch
2. Once via 'pull_request' event

This wastes CI resources by running the same tests twice.

Solution:
- Restrict 'push' trigger to only run on 'main' branch
- Keep 'pull_request' trigger for all PRs
- Maintain 'workflow_call' and 'workflow_dispatch' for manual/reusable workflows

Result:
- Pushes to main: runs once via push event
- Pull requests: runs once via pull_request event
- 50% reduction in CI runs for PRs

Author: jensens

.github/workflows/tests.yaml

@@ -2,10 +2,12 @@ name: Testing
 
 on:
   push:
+    branches:
+      - main
   pull_request:
-   types:
-     - "reopened"
-     - "opened"
+    types:
+      - "reopened"
+      - "opened"
   workflow_call:
   workflow_dispatch:
 

CHANGES.md

@@ -2,7 +2,7 @@
 
 ## 5.0.1 (unreleased)
 
-- Fix: `process_line()` now correctly comments out packages in `override_keys` and `ignore_keys` for both requirements and constraints files. Previously, these settings only applied to constraints files (variety="c"). Now they work for requi## 5.0.0 (2025-10-25)rements files (variety="r") as well, with the message "-> mxdev disabled (version override)" for override_keys in requirements.
+- Chore: Optimize GitHub Actions to prevent duplicate workflow runs on pull requests. Restrict `push` trigger to only run on `main` branch, so PRs only trigger via `pull_request` event. This reduces CI resource usage by 50% for PR workflows.
   [jensens]
 
 ## 5.0.0 (2025-10-25)