Update dependabot.yml to use correct boto3 group

[roger-zhangg]

Which issue(s) does this change fix?

boto3 group not functioning correctly after we changed from boto3 -> boto3[crt], botocore -> botocore[crt], now these dependency updates are creating seperate PRs. This change can make sure the boto3 group updates will be included in a single Depbot PR

Why is this change necessary?

How does it address the issue?

What side effects does this change have?

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Review the generative AI contribution guidelines
• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.