Add ldconfig after libgdiplus installation

Run ldconfig to update the dynamic linker cache after installing libgdiplus,
ensuring the library is properly registered and discoverable by .NET runtime.

Author: claude

.github/workflows/dotnet.yml

@@ -29,6 +29,7 @@ jobs:
       run: |
         sudo apt-get update
         sudo apt-get install -y libgdiplus
+        sudo ldconfig
 
     - name: Run Unit Tests
       run: |