build(deps): bump boto3 from 1.14.43 to 1.15.11 in /src/karmen_backend

Bumps [boto3](https://github.com/boto/boto3) from 1.14.43 to 1.15.11.
- [Release notes](https://github.com/boto/boto3/releases)
- [Changelog](https://github.com/boto/boto3/blob/develop/CHANGELOG.rst)
- [Commits](boto/boto3@1.14.43...1.15.11)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>