CI: Restore only test project to preserve xunit in assets

Restore only the test project (not the main project separately).
The test project restore will also restore the main project as a dependency,
but the shared assets file will include xunit. Restoring the main project
separately overwrites the assets file and removes xunit.

Tested locally - all 92 tests pass.

Author: Alex J Lennon

.github/workflows/ci.yml

@@ -30,7 +30,10 @@ jobs:
       run: rm -rf obj bin
 
     - name: Restore dependencies (explicit xunit)
-      run: dotnet restore InstDotNet.sln
+      run: |
+        # Restore test project - this also restores main project as dependency
+        # and ensures xunit is in the shared assets file
+        dotnet restore tests/InstDotNet.Tests.csproj
       
     - name: Run Tests
       run: dotnet test tests/InstDotNet.Tests.csproj -c Release -p:GitCommitHash=${{ steps.git.outputs.hash }} --no-restore --verbosity normal