Downgrade boto3 (ISD-2999)

[amandahla]

Overview

This PR downgrades boto3 to prevent error while uploading a media.

The user gets an error and in the logs there is the message "An error occurred (MissingContentLength) when calling the PutObject operation: None".

Issue:
boto/boto3#4398

Rationale

Fix integration with S3.

Juju Events Changes

Module Changes

Library Changes

Checklist

• The charm style guide was applied
• The contributing guide was applied
• The changes are compliant with ISD054 - Manging Charm Complexity
• The documentation is generated using src-docs
• The documentation for charmhub is updated.
• The PR is tagged with appropriate label (urgent, trivial, complex)
• The changelog is updated with changes that affect the users of the charm.

[github-actions]

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