Add github actions workflow

.github/workflows/ci_maintainers_toolbox.yml

@@ -0,0 +1,43 @@
+name: "[CI] Maintainers' toolbox"
+on:
+  push:
+    branches:
+      - develop
+      - release/*
+      - "*-stable"
+  pull_request:
+    branches-ignore:
+      - "chore/l10n*"
+
+env:
+  CI: "true"
+  SIMPLECOV: "true"
+  RUBY_VERSION: 2.7.5
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
+jobs:
+  lint:
+    strategy:
+      fail-fast: false
+      matrix:
+        command:
+          - bundle exec rspec
+    name: Lint code
+    runs-on: ubuntu-latest
+    if: "!startsWith(github.head_ref, 'chore/l10n')"
+    timeout-minutes: 60
+    steps:
+      - uses: actions/checkout@v3
+        with:
+          fetch-depth: 1
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ env.RUBY_VERSION }}
+          bundler-cache: true
+      - run: ${{ matrix.command }}
+        name: ${{ matrix.command }}
+        with:
+          working-directory: "decidim-maintainers_toolbox"