actions: use pre-build container

.github/workflows/build_test_firmware.yml

@@ -23,6 +23,7 @@ jobs:
           gcc: ['12.2.Rel1']  # can add other versions if needed
     name: "Build firmware"
     runs-on: ubuntu-latest
+    container: LnnrtS/metamodule:latest
     steps:
       - name: Install Arm GNU Toolchain (arm-none-eabi-gcc)
         uses: carlosperate/arm-none-eabi-gcc-action@v1
@@ -35,14 +36,6 @@ jobs:
           submodules: 'recursive'
           token: ${{ secrets.CHECKOUT_TOKEN }}
 
-      - name: Install linux dependencies
-        run: |
-          sudo apt install -y ninja-build
-
-      - name: Build and install flatbuffer compiler
-        run: |
-          cd firmware/lib/flatbuffers && cmake -S . -B build -DCMAKE_BUILD_TYPE=Release -GNinja && cmake --build build
-
       - name: Build and test
         run: cd firmware && make configure && make all