Don't build when running tests

If the workflow is going to split restore, build, and test into separate
steps, each should use the result of the prior. Build was invoked with
`--no-restore` but test was restoring, building, and then testing.

ci/dotnet.yml

@@ -22,4 +22,4 @@ jobs:
     - name: Build
       run: dotnet build --no-restore
     - name: Test
-      run: dotnet test --no-restore --verbosity normal
+      run: dotnet test --no-build --verbosity normal