linting: install codespell, a spell checker software

linting

@@ -2,6 +2,7 @@ FROM debian:unstable
 
 RUN apt-get update \
 &&  apt-get install --no-install-recommends --no-install-suggests --yes \
+    codespell \
     gir1.2-gdkpixbuf-2.0 \
     gir1.2-poppler-0.18 \
     gir1.2-rsvg-2.0 \