[SF-30] Fix Linear workflow secret guard syntax

[alexanderbrunker-star]

https://linear.app/captain-leopard-ai-engineering/issue/SF-30/fix-github-actions-linear-workflow-secret-guard-syntax

Verification:

• removed unsupported if: ${{ secrets.LINEAR_API_TOKEN != }} usage from both Linear workflows\n- replaced it with workflow-level env.LINEAR_API_TOKEN and job-level if: ${{ env.LINEAR_API_TOKEN != }}\n- confirmed only the two workflow files changed on this branch

[linear]

SF-30 Fix GitHub Actions Linear workflow secret guard syntax

Scope

Repair the GitHub Actions workflow syntax in the Linear sync workflows so GitHub no longer rejects them at parse time.

Problem

GitHub reports:
Invalid workflow file: .github/workflows/linear-pr-sync.yml#L1
Unrecognized named-value: 'secrets'

The current workflows use secrets.LINEAR_API_TOKEN directly in a job-level if: expression, which is not supported in that evaluation context.

Deliverables

• Update .github/workflows/linear-pr-sync.yml
• Update .github/workflows/linear-done-automerge.yml
• Route the secret through workflow env and gate jobs with env.LINEAR_API_TOKEN != ''
• Keep the runtime token available to the scripts

Acceptance

• No workflow file contains if: ${{ secrets.LINEAR_API_TOKEN != '' }}
• The workflows are syntactically valid for GitHub Actions parsing
• PR is opened with the fix on its own branch