Fix workflow failure: Publish step should not fail when no .snupkg exists

[reneschulte]

We successfully publish the NuGet package, but the GitHub Actions workflow still fails in the “Publish to NuGet” step because it tries to push a symbols package (*.snupkg) that is not produced.

Evidence / log excerpt:

• "Your package was pushed."
• then: "File does not exist (Build\nuget*.snupkg)."
• "Error: Process completed with exit code 1."

So the publish succeeded, but the job is marked as failed due to the missing .snupkg.

Goal:
Make the publish step robust:

• Always push Build\nuget*.nupkg (as today)
• Only push Build\nuget*.snupkg if at least one exists
• If no .snupkg exists, skip symbols publishing and keep the job green

Constraints:

• Do NOT change build/pack behavior, versioning, or triggers
• Do NOT switch packaging approach (keep current nuget pack / .nuspec flow)
• Keep using 3rdParty\nuget\nuget.exe and the existing NUGET_API_KEY secret

Implementation notes:
Update the workflow file that contains the publish commands (e.g. .github/workflows/build-nuget.yml). Replace the publish step so it:

1. Fails if no .nupkg exists (this should remain an error)
2. Pushes all .nupkg files found
3. Checks whether any .snupkg exists and only then pushes those; otherwise prints: "No .snupkg found – skipping."

Preferred approach:
Use PowerShell (shell: pwsh) with Get-ChildItem and proper error handling to avoid wildcard behavior in cmd causing non-zero exit codes.

Acceptance criteria:

• Workflow run pushes the .nupkg successfully
• Workflow does not fail when no .snupkg exists
• If a .snupkg exists in Build\nuget, it is pushed as well