Action fails when there are no SAM changes

**Describe the bug**
When a change is pushed to main which doesn't update the SAM template, the deployment job will fail.

**To Reproduce**
Steps to reproduce the behavior:
The previous workflow must have completed successfully, and the repo hasn't been updated.
1. Go to Actions
2. Click on workflow "SAM Validate, Build, Test, Deploy"
3. Choose "Re-run jobs"

This job will fail

**Expected behavior**
The running job should succeed

**Screenshots**
Step "SAM deploy" fails with the following error:
(note that I ran this from my own fork, so the stack name is different to what you will expect)

A possible fix: Change the last command in template.yml to the following:

sam deploy --template-file .aws-sam/build/template.yaml \
--stack-name ${{ steps.vars.outputs.environment }} \
--s3-bucket ${{ steps.vars.outputs.environment }} \
--parameter-overrides \
'ParameterKey=Name,ParameterValue=example \
ParameterKey=Version,ParameterValue=${{ steps.vars.outputs.version }}' \
--capabilities CAPABILITY_IAM CAPABILITY_NAMED_IAM \
|| echo "Nothing to deploy, no changes"

从 template.yml 和“SAM Validate, Build, Test, Deploy”工作流开始，重点关注失败的“SAM deploy”步骤。通过在不更改 SAM template 的情况下重新运行一个已完成的工作流来重现该失败，然后验证在没有要部署的内容时，job 能够成功并报告没有部署更改。

由索引模型根据 Issue 内容生成。