Bump GitHub Actions major versions across push and PR workflows

[Copilot]

This PR packages the already-applied GitHub Actions dependency upgrades from master into a reviewable PR and extends the same version alignment to the PR workflow file. It updates action references to current major versions in both workflow YAMLs.

• Scope

  • Updated workflow action versions in:
    • .github/workflows/push-main.yml
    • .github/workflows/pull-requests.yml

• Action version upgrades

  • actions/checkout: v3 → v7
  • actions/setup-dotnet: v3 → v5
  • actions/upload-pages-artifact: v1 → v5 (push-main)
  • actions/deploy-pages: v1 → v5 (push-main)

• Dependabot config

  • No changes to .github/dependabot.yml (it currently configures NuGet updates only, not GitHub Actions).

# Example of the applied pattern
- uses: actions/checkout@v7
- name: Setup .NET
  uses: actions/setup-dotnet@v5