Add an Actions workflow for CI against multiple Ruby verisons

.github/ISSUE_TEMPLATE.md

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+## Does This Really Belong to GitHub issues?
+
+If you find a bug you understand well, poor default, incorrect or unclear piece of documentation,
+or missing feature, please [file an
+issue](http://github.com/ruby-amqp/bunny/issues) on GitHub.
+
+Please use [Bunny's mailing list](http://groups.google.com/group/ruby-amqp) for questions,
+investigations, and discussions. GitHub issues should be used for specific, well understood, actionable
+maintainers and contributors can work on.
+
+When filing an issue, please specify
+
+ * Which Bunny and RabbitMQ versions are used
+ * Recent RabbitMQ log file contents
+ * Full exception stack traces
+ * Steps to reproduce or a failing test case
+
+This would greatly help the maintainers help you.

.github/workflows/ci.yml

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+name: Ruby CI
+
+on:
+  push:
+    branches:
+      - "main"
+  pull_request:
+    branches:
+      - "main"
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    strategy:
+      matrix:
+        ruby-version:
+          - "3.4.2"
+          - "3.3.7"
+          - "3.2.7"
+
+    steps:
+      - uses: actions/checkout@v4
+      - name: Set up Ruby ${{ matrix.ruby-version }}
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby-version }}
+      - name: Install dependencies
+        run: bundle install
+      - name: Run tests
+        run: bundle exec rspec -c