Wire CI workflow to build.ps1 across OS matrix

[atifaziz]

Objective

Update GitHub Actions CI to execute the new scripted Build/Test/Pack pipeline (including Roslyn 4.4 artifacts) on all matrix environments.

Scope

• Replace direct dotnet build/test/pack calls with dotnet pwsh ./build.ps1 equivalents.
• Preserve existing version suffix behavior in pack stage.
• Ensure tool restore order supports dotnet pwsh on Windows and Linux runners.

Files

• .github/workflows/ci.yml

Tasks

• Update Build step:
  • Replace existing build command with dotnet pwsh ./build.ps1 -Configuration Release.
• Update Test step:
  • Replace existing test command with dotnet pwsh ./build.ps1 -Test -NoBuild -Configuration Release.
• Update Pack step:
  • Keep current suffix logic.
  • Replace pack command with dotnet pwsh ./build.ps1 -Pack -Configuration Release -VersionSuffix $versionSuffix.
• Verify dotnet tool restore occurs before Build/Test/Pack steps in all applicable jobs.

Acceptance Criteria

• CI builds succeed on windows-* and ubuntu-* matrix entries.
• Build and Test phases execute via build.ps1 only.
• Pack phase uses script and still applies version suffix logic correctly.

Dependencies

• Depends on Issue Add build.ps1 for multi-Roslyn Build/Test/Pack orchestration #208.

Notes

• Keep workflow changes minimal and avoid unrelated pipeline refactors.

[atifaziz]

Closed via PR #214.