[aws] ci deploy branch changes existing function configuration

When executing a CI build (step `branch-deploy`), one can see that the function configuration is updated:

https://app.circleci.com/pipelines/github/adobe/helix-s3r2-sync/575/workflows/988a84ff-7b27-4d21-b046-c8a4b2ca50ff/jobs/1257

Look for the line:
```
updating existing Lambda function configuration helix-services--s3r2-sync
```

in code this happens here:

https://github.com/adobe/helix-deploy/blob/04c455a20ac778e0838ef0fc8156f9aab510e095/src/deploy/AWSDeployer.js#L267

I think this causes newly started function invocations of the `main` function to use that CI configuration, which is unexpected.

cc: @stefan-guggisberg

Start with src/deploy/AWSDeployer.js around line 267 and trace the branch-deploy path that produces the CircleCI message about updating the existing Lambda function configuration. Compare how the CI configuration relates to the main function invocation. Done means branch deployment no longer unexpectedly changes the main function's configuration.

Written by the indexing model from the issue text.