ci: build CI to ensure the local package always works

this tests in two ways:
- install the package locally in each major os/architecture combination
  supported by GitHub Actions, then run `editorconfig-checker --version`
  like `run-tests.sh` does
- running `run-tests.sh` once in an ubuntu machines

The workflow is triggered both by pushes to any of the branches and for
each pull request.

Author: klaernie

.github/workflows/ci.yaml

@@ -0,0 +1,52 @@
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
+
+permissions: read-all
+
+jobs:
+  test-architectures:
+    name: test OS/arch combinations
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - 'ubuntu-24.04'
+          - 'ubuntu-24.04-arm'
+          - 'macos-13' # the last intel mac
+          - 'macos-15' # arm64 mac
+          - 'windows-2025'
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: install local package
+        run: |
+          python -m pip install .
+
+      - name: test that editorconfig-checker works by letting it output it's version
+        run: |
+          ec --version
+
+
+  test-python-versions:
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: install flake8
+        run: |
+          python -m pip install flake8
+
+      - name: run testsuite verifying against all python versions
+        shell: bash
+        run: |
+          # only test the local package, since we assume that we only
+          # upload to PyPI once we are certain that the local package is fine
+          export TEST_LOCAL_PKG=true
+          export TEST_PYPI_PKG=false
+
+          make test