Add workflow_dispatch event to dotnet.yml for manual workflow triggering

[Copilot]

This PR adds the workflow_dispatch event to the .github/workflows/dotnet.yml workflow to enable manual triggering from the GitHub Actions UI.

Changes Made

• Added workflow_dispatch: event trigger to the on: section of the dotnet.yml workflow
• Added explanatory comment following the same pattern as the existing push-nuget.yml workflow

Benefits

• Enables a "Run workflow" button in the GitHub Actions tab
• Allows developers to manually trigger the .NET build and test workflow without requiring a push or pull request
• Provides flexibility for testing workflow changes or running builds on-demand

Implementation Details

The change follows the existing pattern established in push-nuget.yml and is minimal - only 2 lines added:

on:
  push:
    branches: [ master ]
  pull_request:
    branches: [ master ]
  # Allows you to run this workflow manually from the Actions tab
  workflow_dispatch:

This maintains all existing functionality while adding the manual trigger capability requested.

This pull request was created as a result of the following prompt from Copilot chat.

Voeg de mogelijkheid toe om de workflow via de GitHub UI te triggeren door de 'workflow_dispatch' event toe te voegen aan de dotnet.yml workflow. Dit zorgt ervoor dat er een 'Run workflow'-knop beschikbaar wordt in de Actions-tab, waarmee de workflow handmatig kan worden gestart.

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