Drop pull_request trigger from version_command workflow

[TomasVotruba]

Removes the pull_request trigger from the version_command workflow.

Why

The job runs composer require symplify/easy-coding-standard from Packagist, then asserts ecs --version prints the PHP-CS-Fixer line — a smoke test of the published scoped+downgraded artifact (guards #8).

On pull_request it installs the currently-published package, not the PR code — so the result is identical regardless of the diff. It never tests the change, yet the fresh, uncached composer require makes it one of the slowest jobs on every PR.

The push (main + tags) and weekly schedule triggers already cover the published artifact, which is the only thing this test can actually catch drift in.

Change

 on:
-    pull_request:
     push:
         branches:
             - main
         tags:
             - '*'
     schedule:
         -   cron: '0 6 * * 1'