Update the Github CI workflow to include Puppet 6 testing

Author: seanmil

.github/workflows/main.yml

@@ -54,6 +54,24 @@ jobs:
         run: docker build . --file Dockerfile --tag octocatalog-diff:ruby${{matrix.ruby-version}} --build-arg RUBY_VERSION=${{matrix.ruby-version}}-stretch
       - name: Tests
         run: docker run -e PUPPET_VERSION -e PUPPET_VERSIONS -e RSPEC_TEST -e RUBOCOP_TEST -e ENFORCE_COVERAGE octocatalog-diff:ruby${{matrix.ruby-version}} /app/script/cibuild
+
+  puppet-6-18-0:
+    env:
+      PUPPET_VERSIONS: "6.18.0"
+      PUPPET_VERSION: "6.18.0"
+      RUBOCOP_TEST: false
+      RSPEC_TEST: true
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby-version: ["2.5", "2.6"]
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v1
+      - name: Build container
+        run: docker build . --file Dockerfile --tag octocatalog-diff:ruby${{matrix.ruby-version}} --build-arg RUBY_VERSION=${{matrix.ruby-version}}-stretch
+      - name: Tests
+        run: docker run -e PUPPET_VERSION -e PUPPET_VERSIONS -e RSPEC_TEST -e RUBOCOP_TEST -e ENFORCE_COVERAGE octocatalog-diff:ruby${{matrix.ruby-version}} /app/script/cibuild
       - name: Rubocop and Coverage
         run: docker run -e PUPPET_VERSION -e PUPPET_VERSIONS -e RSPEC_TEST -e RUBOCOP_TEST -e ENFORCE_COVERAGE octocatalog-diff:ruby${{matrix.ruby-version}} /app/script/cibuild
         if: matrix.ruby-version == '2.6'