Compile at least one CI build as debug

.github/workflows/build.yml

@@ -72,7 +72,7 @@ jobs:
 
       - name: Build
         run: |
-          cmake . -DBUILD_EXAMPLES=1 -DUSE_SDL2=ON
+          cmake . -DBUILD_EXAMPLES=1 -DUSE_SDL2=ON -DCMAKE_BUILD_TYPE=Debug
           make -j2
 
       - name: Test (headless)