GitHub Action for automatic test builds of the firmware

[retrofun]

My changes for a system status page introduced compile errors for older versions of gcc and were fixed here. Newer gcc versions accept new syntax constructs and thus hide such errors.

This can be prevented in the future with automatic test builds of the firmware.

I've built a Docker image with the (aged) build environment/cross compiler created by install_arm-none-eabi-gcc.sh. A ready-built public Docker image to build the firmware is available at the GitHub Container Registry: ghcr.io/retrofun/mist-firmware:builder.

Repository for the Dockerfile to create the Docker image is docker-mist-firmware-builder.

Results of automatic test builds with GitHub Actions on push can be seen in my two test branches

• github-actions-test: Failure, red cross @ 'Add test-build action' commit
• github-actions-test-2: Success, green checkmark @ 'Add test-build action' commit

Click on red cross / green checkmark for details!

For mist-firmware repository it should be sufficient to cherry-pick the 'Add test-build action' commit (file .github/workflows/test-build.yaml).

Or create an own Docker image, publish it as package for mist-devel, change the image URL in the test-build.yaml file and add it to the repository.

[gyurco]

I'm not proficient in GitHub actions, but if it can be used with only a single YAML file, then why not?
But as there are only about 2 regular contributors, I don't know if it's a really big help :)

[jotego]

It is true that, as @gyurco said, if the two regular contributors are already set, this may not be of much help. But the action file is also a way to document the tool chain to build the firmware. And the docker files will ease setup for the occasional user.

@retrofun would you consider making a PR?