Github Actions: Try to fix build

Change-Id: I495df3b7e644b3ebe358a6cfd2e12c14b8f1fbfc

Author: bahusoid

.github/workflows/build.yml

@@ -42,7 +42,7 @@ jobs:
     - name: make it all
       run: |
         sudo apt-get update
-        sudo apt-get install automake bison build-essential ccache flex libc6-dev libgmp3-dev libmpfr-dev libsdl1.2-dev libtool-bin texinfo zip gawk wget libmpc-dev gettext
+        sudo apt-get install automake bison build-essential ccache flex libc6-dev libgmp3-dev libmpfr-dev libsdl1.2-dev libtool-bin texinfo zip gawk wget libmpc-dev gettext gtk-doc-tools
         cd tools
         chmod +x rockboxdev.sh
         sudo ./rockboxdev.sh --target=${{matrix.arch}}