Remove Azure-dependent CI steps to fix forked PR builds

[Copilot]

Forked PRs fail CI because Azure secrets (AZURE_CLIENT_ID, AZURE_TENANT_ID, etc.) are not available to fork workflows, causing azure/login@v2 to abort the entire job.

Changes

• Removed Azure Login via OIDC step (azure/login@v2)
• Removed Sign packages step (NuGetKeyVaultSignTool with Azure Key Vault)

All other steps — checkout, dotnet setup, build/test, push, and artifact upload — remain intact.

Original prompt

Create a pull request in LuckyPennySoftware/MediatR to fix CI failures on forked pull requests by removing Azure-dependent steps entirely (no conditional execution).

Context:

• The CI job failed with Azure login error: Using auth-type: SERVICE_PRINCIPAL. Not all values are present. Ensure 'client-id' and 'tenant-id' are supplied.
• Failing run/job: https://github.com/LuckyPennySoftware/MediatR/actions/runs/22280245606/job/64449713651?pr=1149
• Workflow file at failing ref: .github/workflows/ci.yml

Required changes:

1. Edit .github/workflows/ci.yml to remove the following steps from the build job:
   • Azure Login via OIDC step using azure/login@v2 (client-id / tenant-id / subscription-id inputs)
   • Sign packages step that runs NuGetKeyVaultSignTool sign ... --azure-key-vault-managed-identity ...
2. Do not add if: conditions or other gating logic; the steps should be deleted.
3. Ensure the workflow still builds/tests and uploads artifacts successfully.

Notes:

• Leave other steps intact (checkout, setup-dotnet, install tool, build/test, push, upload artifact).
• Verify YAML remains valid and indentation correct after removing steps.

This pull request was created from Copilot chat.

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.