Update testbed docker image

* Update base image to Ubuntu 24.10. This uses a python version where j2cli no
  longer works when installed using pip so use the version from Ubuntu instead
  which has been patched to work.

* Update shellcheck, pylint, pytest, isort, flake8, black and yamllint to the
  latest versions. This closes #502.

* Use a longer expect timeout to fix tests failing when gpg is killed due to
  this timeout.

* Explicitly flush gpg-agent's cached passwords to fix failing tests with
  latest gnupg. Also clean up after tests to avoid having gpg-agents running
  after the test (e.g. when running tests directly without docker).

test/pinentry-mock

@@ -6,10 +6,9 @@
 echo "OK Pleased to meet you"
 while read -r line; do
   if [[ $line =~ GETPIN ]]; then
-    password="$(cat /tmp/mock-password 2>/dev/null)"
+    password="$(cat "$GNUPGHOME/mock-password" 2>/dev/null)"
     if [ -n "$password" ]; then
-      echo -n "D "
-      echo "$password"
+      echo "D $password"
       echo "OK";
     else
       echo "CANCEL";