Configure pylint to run only on pull requests

[Copilot]

Pylint currently runs on every push, causing unnecessary CI overhead. This changes the trigger to pull requests only.

Changes

• Workflow trigger: Changed code-check.yml from on: [push] to on: [pull_request]

# Before
on: [push]

# After  
on: [pull_request]

Release workflows retain lint checks for tag-based publishing.

Original prompt

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This section details on the original issue you should resolve

<issue_title>pylint only on pull requests</issue_title>
<issue_description>now pylint is launched on every activity</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes pylint only on pull requests #13

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