[6.0] a8b11a96a Remove stretch as its EOL

[Dridi Boukelmoune]

commit a8b11a96abed2f8b3150905ac6cdb0b1330f3447
Author: Simon Stridsberg <simon.stridsberg at varnish-software.com>
Date:   Mon Nov 13 21:42:40 2023 +0100

    Remove stretch as its EOL

diff --git a/.circleci/config.yml b/.circleci/config.yml
index 0214e77c8..97e0ac01a 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -436,7 +436,6 @@ workflows:
                 - ubuntu:bionic
                 - ubuntu:focal
                 - ubuntu:jammy
-                - debian:stretch
                 - debian:buster
                 - debian:bullseye
                 - debian:bookworm