ci: add flex and bison

.gitlab-ci.yml

@@ -20,7 +20,7 @@ cache:
 build:
   stage: build
   before_script:
-    - apt-get update && apt-get install -y git g++ cmake ninja-build doxygen
+    - apt-get update && apt-get install -y git g++ cmake ninja-build doxygen bison flex
   script:
     - mkdir -p ${BUILD_DIR}                       # Create build directory
     - cmake -S . -B ${BUILD_DIR} -G Ninja         # configures the project