unix: update Debian snapshot

It's been a while since we've refreshed the Debian snapshot. Might as
well do that now.

Author: indygreg

cpython-unix/base.Dockerfile

@@ -18,7 +18,7 @@ CMD ["/bin/bash", "--login"]
 WORKDIR '/build'
 
 RUN for s in debian_jessie debian_jessie-updates debian-security_jessie/updates; do \
-      echo "deb http://snapshot.debian.org/archive/${s%_*}/20210404T083057Z/ ${s#*_} main"; \
+      echo "deb http://snapshot.debian.org/archive/${s%_*}/20210927T204628Z/ ${s#*_} main"; \
     done > /etc/apt/sources.list && \
     ( echo 'quiet "true";'; \
       echo 'APT::Get::Assume-Yes "true";'; \

cpython-unix/build.cross.Dockerfile

@@ -18,7 +18,7 @@ CMD ["/bin/bash", "--login"]
 WORKDIR '/build'
 
 RUN for s in debian_stretch debian_stretch-updates debian-security_stretch/updates; do \
-      echo "deb http://snapshot.debian.org/archive/${s%_*}/20210404T083057Z/ ${s#*_} main"; \
+      echo "deb http://snapshot.debian.org/archive/${s%_*}/20210927T204628Z/ ${s#*_} main"; \
     done > /etc/apt/sources.list && \
     ( echo 'quiet "true";'; \
       echo 'APT::Get::Assume-Yes "true";'; \