improve github CI definitions #317

	# Build dub on Alpine Linux, testing compatibility with Musl
	name: Alpine

	on:
	pull_request:
	branches:
	- master
	- stable
	paths-ignore:
	- 'changelog/**'
	push:
	branches:
	- master
	- stable
	# Use this branch name in your fork to test changes
	- github-actions

	jobs:
	main:
	name: Run
	strategy:
	# Default, disable if you want to debug
	fail-fast: false
	matrix:
	include:
	# Disabled as we rely on DIP1000 `foreach (scope)` which GDC < 12 doesn't support
	# - { dc: gdc, dcpkg: gcc-gdc, dcbin: gdc }
	- { dc: ldc, dcpkg: ldc, dcbin: ldc2 }
	- { dc: dmd, dcpkg: dmd, dcbin: dmd }

	# OS doesn't matter, we just need Docker
	runs-on: ubuntu-latest
	steps:
	# Checkout the repository
	- name: Checkout
	uses: actions/checkout@v3

	- name: Build
	run: \|
	docker build -t alpine-dub-image \
	--build-arg="DCPKG=${{ matrix.dcpkg}}" \
	--build-arg="DCBIN=${{ matrix.dcbin}}" \
	-f docker/Dockerfile.alpine $(pwd)

	- name: Test
	run: docker run alpine-dub-image

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