ci: Install SDL2

Author: chadowo

.github/workflows/build.yml

@@ -10,7 +10,7 @@ jobs:
       - uses: actions/checkout@v3
 
       - name: Install dependencies
-        run: sudo apt-get update && sudo apt-get install libmruby-dev
+        run: sudo apt-get update && sudo apt-get install libmruby-dev libsdl2-dev
 
       - name: Configure CMake
         run: cmake -S . -B build