build: Add rspec to CI (#22)

Adds our rspec test suite to our CI pipeline.

.github/workflows/rspec.yml

@@ -0,0 +1,26 @@
+name: Ruby
+
+on:
+  push:
+    branches:
+      - main
+      - release-*
+  pull_request:
+
+jobs:
+  rspec:
+
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        ruby-version: ['2.7', '3.0', '3.1', '3.2']
+
+    steps:
+    - uses: actions/checkout@v3
+    - name: Set up Ruby
+      uses: ruby/setup-ruby@v1
+      with:
+        ruby-version: ${{ matrix.ruby-version }}
+        bundler-cache: true
+    - name: Run tests
+      run: bundle exec rspec