[Bug]: Push image to GHCR incorrectly runs in PR

[ChrisPC-39]

🐞 Bug Summary

PR validation step "Push image to GHCR" fails because it's supposed to only run on the main branch. The Github Action should be fixed in order to skip this step while validating a PR.

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🧩 Affected Component

Select the area of the project impacted:

• mcpgateway - API
• mcpgateway - UI (admin panel)
• mcpgateway.wrapper - stdio wrapper
• Federation or Transports
• CLI, Makefiles, or shell scripts
• Container setup (Docker/Podman/Compose)
• Other (explain below)

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🔁 Steps to Reproduce

1. Create a PR from any branch
2. Wait for "build-scan-sign" to run and fail

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🤔 Expected Behavior

Step should be skipped.

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📓 Logs / Error Output

denied: installation not allowed to Write organization package
Error: Process completed with exit code 1.