👷 add test step

Author: nlohmann

.github/workflows/ccpp.yml

@@ -13,5 +13,7 @@ jobs:
       run: mkdir build
     - name: cmake
       run: cd build ; cmake ..
-    - name: make
+    - name: build
       run: make -C build
+    - name: test
+      run: cd build ; ctest -j 10