Update dependency boto3 to v1.21.0 (develop)

This MR contains the following updates:

Package	Type	Update	Change
boto3	dependencies	minor	==1.20.53 -> ==1.21.0

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Release Notes

boto/boto3

v1.21.0

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• api-change:appflow: [botocore] Launching Amazon AppFlow SAP as a destination connector SDK.
• feature:Parser: [botocore] Adding support for parsing int/long types in rest-json response headers.
• api-change:rds: [botocore] Adds support for determining which Aurora PostgreSQL versions support Babelfish.
• api-change:athena: [botocore] This release adds a subfield, ErrorType, to the AthenaError response object in the GetQueryExecution API when a query fails.

v1.20.54

Compare Source

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• api-change:ssm: [botocore] Documentation updates for AWS Systems Manager.

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