Lint our YAML files, using yamllint

Let's try using GitHub Actions for this task, instead of the usual
CircleCI. We can always move it later, if need be.

Author: bquorning

.circleci/config.yml

@@ -72,7 +72,9 @@ jobs:
       - run:
           name: Setup Code Climate test-reporter
           command: |
-            curl -L https://codeclimate.com/downloads/test-reporter/test-reporter-latest-linux-amd64 > ./cc-test-reporter
+            curl -L \
+              https://codeclimate.com/downloads/test-reporter/test-reporter-latest-linux-amd64 > \
+              ./cc-test-reporter
             chmod +x ./cc-test-reporter
       - run:
           name: Run specs
@@ -87,7 +89,8 @@ workflows:
     jobs:
       - confirm_config_and_documentation
 
-      # Use `requires: [confirm_config_and_documentation]` to trick Circle CI into starting the slow jruby job early.
+      # Use `requires: [confirm_config_and_documentation]` to trick Circle CI into starting the slow
+      # jruby job early.
       - rspec:
           requires: [confirm_config_and_documentation]
           matrix:

.github/workflows/linting.yml

@@ -0,0 +1,15 @@
+name: Linting
+on:
+  - pull_request
+jobs:
+  yamllint:
+    name: Yamllint
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Yamllint
+        uses: karancode/yamllint-github-action@master
+        with:
+          yamllint_comment: true
+        env:
+          GITHUB_ACCESS_TOKEN: ${{ secrets.GITHUB_TOKEN }}

.rubocop.yml

@@ -1,9 +1,9 @@
 inherit_from: .rubocop_todo.yml
 
 require:
- - rubocop-performance
- - rubocop-rspec
- - rubocop/cop/internal_affairs
+  - rubocop-performance
+  - rubocop-rspec
+  - rubocop/cop/internal_affairs
 
 AllCops:
   DisplayCopNames: true

.yamllint

@@ -0,0 +1,11 @@
+extends: default
+
+rules:
+  comments:
+    min-spaces-from-content: 1
+  document-start: disable
+  line-length:
+    allow-non-breakable-inline-mappings: true
+    max: 100
+  truthy:
+    check-keys: false