Expand linting GitHub Actions Workflow to include oldstable, unstable container images

[atc0005]

Currently the code is linted using the "stable" index.docker.io/atc0005/go-ci:go-ci-lint-only container in two different workflows:

• send2teams/.github/workflows/lint-and-test-only.yml

  Lines 8 to 22 in 171c451

  	name: Quick Validation
  	# Run builds for Pull Requests (new, updated)
  	# `synchronized` seems to equate to pushing new commits to a linked branch
  	# (whether force-pushed or not)
  	on:
  	push:
  	jobs:
  	lint_and_test_code:
  	name: Lint and test using latest stable container
  	runs-on: ubuntu-latest
  	timeout-minutes: 10
  	container:
  	image: index.docker.io/atc0005/go-ci:go-ci-lint-only

• send2teams/.github/workflows/lint-and-build-code.yml

  Lines 8 to 24 in 171c451

  	name: Validate Codebase
  	# Run builds for Pull Requests (new, updated)
  	# `synchronized` seems to equate to pushing new commits to a linked branch
  	# (whether force-pushed or not)
  	on:
  	#push:
  	pull_request:
  	types: [opened, synchronize]
  	jobs:
  	lint_code:
  	name: Lint codebase
  	runs-on: ubuntu-latest
  	timeout-minutes: 10
  	container:
  	image: index.docker.io/atc0005/go-ci:go-ci-lint-only

The first workflow is meant as a quick validation check (linting & tests) on push. The second, more comprehensive workflow is used on pull requests only and applies linting, test & build jobs. The tests and builds are performed using three different containers:

• oldstable
• stable
• unstable

I plan to extend this second workflow to also use the unstable image in linting checks. I don't yet see the value in linting using the oldstable image also, but will include it also just to "cover the bases".

Based on recent GHAW runs, I expect that the unstable image will generate numerous linting complaints as I test out more strict linting options in that image. Based on this, I will refrain from setting linting results for that container as required "OK" before allowing merges. This may require adding a second GHAW job to run the linting checks using that container so that the existing Validate Codebase results remain unaffected (this GHAW is required to pass).