Switch to ghcr cross docker image and download Python 3.8

Author: messense

examples/namespace_package/Dockerfile

@@ -1,13 +1,10 @@
 FROM quay.io/pypa/manylinux2014_aarch64 AS manylinux
 
-FROM rustembedded/cross:aarch64-unknown-linux-gnu
-
-RUN apt-get update && \
-    apt-get install -y software-properties-common && \
-    add-apt-repository ppa:deadsnakes/ppa && \
-    apt-get update && \
-    apt-get install -y python3.8 && \
-    update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.8 1
+FROM ghcr.io/cross-rs/aarch64-unknown-linux-gnu:edge
+
+RUN curl -L https://github.com/indygreg/python-build-standalone/releases/download/20220318/cpython-3.8.13+20220318-x86_64-unknown-linux-gnu-install_only.tar.gz | tar -xz -C /usr/local
+
+ENV PATH=/usr/local/python/bin:$PATH
 
 COPY --from=manylinux /opt/_internal /opt/_internal
 COPY --from=manylinux /opt/python /opt/python