CI: Explicitly restore xunit before running tests

Add explicit restore step to ensure xunit is available in assets file
before running tests. This ensures xunit dependencies are properly
resolved and available during the build phase.

Sequence:
1. Clean obj/bin
2. Explicitly restore test project (ensures xunit in assets)
3. Run tests with --no-restore (uses pre-restored dependencies)

Tested locally - all 92 tests pass.

Author: Alex J Lennon

.github/workflows/ci.yml

@@ -29,8 +29,11 @@ jobs:
     - name: Clean build artifacts
       run: rm -rf obj bin
 
+    - name: Restore dependencies (explicit xunit)
+      run: dotnet restore tests/InstDotNet.Tests.csproj
+      
     - name: Run Tests
-      run: dotnet test tests/InstDotNet.Tests.csproj -c Release -p:GitCommitHash=${{ steps.git.outputs.hash }} --verbosity normal
+      run: dotnet test tests/InstDotNet.Tests.csproj -c Release -p:GitCommitHash=${{ steps.git.outputs.hash }} --no-restore --verbosity normal
       continue-on-error: false
 
   build: