chore: pin GitHub Actions to SHA hashes

[simonlet]

Summary

• Pin all GitHub Actions references to specific SHA commits instead of mutable version tags
• Prevents supply chain attacks where a tag could be moved to point to malicious code

Test plan

• Pin and allow pinned version of Core-EDC Github actions from our fork of the Core-EDC .github repo
  • e.g. the hash of the tags: [0.11.1_2025-03-10_2, 0.14.0_2025-08-21_2, 0.15.0_2025-12-05_2]
• Verify CI workflows still run correctly after the pin

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