chore: update project file references in Windows workflow

Author: onecoolx

.github/workflows/windows-cpp.yml

@@ -27,12 +27,12 @@ jobs:
       run: ./build_windows.bat
 
     - name: Restore Project
-      run: msbuild ./proj/picasso.sln /t:Restore /p:Configuration=$env:Configuration
+      run: msbuild ./proj/picasso.slnx /t:Restore /p:Configuration=$env:Configuration
       env:
         Configuration: ${{ matrix.configuration }}
 
     - name: Build Solution
-      run: msbuild ./proj/picasso.sln /p:Configuration=$env:Configuration
+      run: msbuild ./proj/picasso.slnx /p:Configuration=$env:Configuration
       env:
         Configuration: ${{ matrix.configuration }}