CI: Restore solution to ensure xunit is available

Restore the solution file instead of just the test project to ensure
both projects are restored together. This ensures xunit is properly
included in the shared assets file before building/running tests.

Tested locally - all 92 tests pass.

Author: Alex J Lennon

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
       run: rm -rf obj bin
 
     - name: Restore dependencies (explicit xunit)
-      run: dotnet restore tests/InstDotNet.Tests.csproj
+      run: dotnet restore InstDotNet.sln
 
     - name: Run Tests
       run: dotnet test tests/InstDotNet.Tests.csproj -c Release -p:GitCommitHash=${{ steps.git.outputs.hash }} --no-restore --verbosity normal