Bump boto3 from 1.42.88 to 1.42.91 in /dynamodb

Bumps [boto3](https://github.com/boto/boto3) from 1.42.88 to 1.42.91.
- [Release notes](https://github.com/boto/boto3/releases)
- [Commits](boto/boto3@1.42.88...1.42.91)

---
updated-dependencies:
- dependency-name: boto3
  dependency-version: 1.42.91
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

dynamodb/requirements.txt

@@ -1 +1 @@
-boto3==1.42.88
+boto3==1.42.91