Specify the git ref to checkout during deploy (#95)

When triggering jobs with `workflow_run` the default git ref to fetch
is the default branch[0], causing all deploys to use the dev branch.
Override the default ref with the name of the environment in order
to deploy from the corresponding branch.

[0] https://docs.github.com/en/actions/writing-workflows/choosing-when-your-workflow-runs/events-that-trigger-workflows#workflow_run

.github/workflows/aws-deploy.yaml

@@ -38,6 +38,8 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v3
+        with:
+          ref: ${{ inputs.environment }}
       - name: Install AWS CLI
         run: sudo snap install aws-cli --classic
       - name: Install AWS CDK CLI