Add mend scanning. Update test and release actions

.github/workflows/testing.yml

@@ -0,0 +1,25 @@
+name: Testing
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  spec_tests:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby-version:
+          - '2.7'
+          - '3.0'
+          - '3.1'
+    steps:
+    - uses: actions/checkout@v3
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby-version }}
+        bundler-cache: true # runs 'bundle install' and caches installed gems automatically
+    - name: Run spec tests
+      run: bundle exec rake test