Deploy CI on aarch64

[dboreham]

We have had several cases where stacks don't build, or sometimes don't run, on ARM. e.g. #565

If we had CI running on an aarch64 machine, these failures would be more easily identified in advance.

[dboreham]

It turns out when I deployed our Gitea stack on an arm machine, jobs fail because...the setup-python GitHub action does not support arm (at all, on linux). See: actions/setup-python#705

[dboreham]

I was able to get our actions to run on arm eventually by using the deadsnakes action. That in turn required some changes to our runner image:

diff --git a/gitea/Dockerfile.task-executor b/gitea/Dockerfile.task-executor
index ad5cc64..9b27772 100644
--- a/gitea/Dockerfile.task-executor
+++ b/gitea/Dockerfile.task-executor
@@ -1,5 +1,8 @@
 FROM ubuntu:22.04

+# Set system time zone to prevent the tzdata package from hanging looking for user input pater
+RUN ln -snf /usr/share/zoneinfo/$CONTAINER_TIMEZONE /etc/localtime && echo $CONTAINER_TIMEZONE > /etc/timezone
+
 # Install basic tools
 RUN apt update && apt install -y gpg curl apt-transport-https ca-certificates lsb-release build-essential

@@ -24,3 +27,7 @@ RUN set -uex; \

 # Install Docker
 RUN apt update && apt install -y docker-ce && rm -rf /var/lib/apt/lists/*
+# Install sudo because some actions projects assume it is present, and it is present in GitHub runners
+RUN apt update && apt install -y sudo
+# Install software-properties-common so we have the add-apt-repository command, used by some actions to add a package repo
+RUN apt update && apt install -y software-properties-common

Then I made this change to an example job:

      - name: "Install Python"
        uses: deadsnakes/action@v3.0.1
        with:
          python-version: '3.8'

[dboreham]

Test job passed:

[dboreham]

RUNNER_ARCH=ARM64

[dboreham]

With this PR merged all our CI jobs will run on ARM, if a suitable runner is provisioned.