Fix target arch

Signed-off-by: Piet Gömpel <[email protected]>

Author: Pietfried

docker/images/build-env-base/Dockerfile

@@ -34,9 +34,8 @@ ENV DOXYGEN_VERSION=1.9.8+ds-2.1
 # ARM64 overrides
 RUN if [ "$TARGETARCH" = "arm64" ]; then \
         export NINJA_BUILD_VERSION=1.12.1-1+b1; \
-    fi
-
-RUN apt update \
+    fi && \
+    apt update \
     && apt install --no-install-recommends -y \
     # basic command line tools
     git=${GIT_VERSION} \