ci: add conditionals for docs-only checks

[medubelko]

Add conditionals to skip required checks and unnecessary operations.

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• I've followed the contribution guidelines.
• I've signed the CLA.
• I've successfully run make lint && make test.
• I've added or updated any relevant documentation.
• In documents I changed, I added a meta description if one was missing.
• I've updated the relevant release notes.

[Copilot]

Pull request overview

Adds a path-based filter stage to the QA workflow so downstream lint/test reusable workflows can conditionally skip work (intended for docs-only changes) while still reporting required check results.

Changes:

• Introduces a filter job using dorny/paths-filter to detect whether “source files” changed.
• Wires the filter result into the existing lint and test reusable workflow calls via a source-files input.

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