chore(deps): update dependency boto3 to v1.12.21 (#3099)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [boto3](https://togithub.com/boto/boto3) | patch | `==1.12.18` -> `==1.12.21` |

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### Release Notes

<details>
<summary>boto/boto3</summary>

### [`v1.12.21`](https://togithub.com/boto/boto3/blob/master/CHANGELOG.rst#&#8203;11221)

[Compare Source](https://togithub.com/boto/boto3/compare/1.12.20...1.12.21)

=======

-   api-change:`appconfig`: [``botocore``] Update appconfig client to latest version

### [`v1.12.20`](https://togithub.com/boto/boto3/blob/master/CHANGELOG.rst#&#8203;11220)

[Compare Source](https://togithub.com/boto/boto3/compare/1.12.19...1.12.20)

=======

-   api-change:`lex-models`: [``botocore``] Update lex-models client to latest version
-   api-change:`securityhub`: [``botocore``] Update securityhub client to latest version
-   api-change:`ec2`: [``botocore``] Update ec2 client to latest version
-   api-change:`apigatewayv2`: [``botocore``] Update apigatewayv2 client to latest version
-   api-change:`iot`: [``botocore``] Update iot client to latest version

### [`v1.12.19`](https://togithub.com/boto/boto3/blob/master/CHANGELOG.rst#&#8203;11219)

[Compare Source](https://togithub.com/boto/boto3/compare/1.12.18...1.12.19)

=======

-   api-change:`efs`: [``botocore``] Update efs client to latest version
-   api-change:`redshift`: [``botocore``] Update redshift client to latest version

</details>

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Author: renovate-bot

storage/s3-sdk/requirements.txt

@@ -1 +1 @@
-boto3==1.12.18
+boto3==1.12.21