Upgrade flake8 version for better python linting

[sacOO7]

• Current flake8 version used for linting is ^3.9.2.
• Latest version of flake8 is 7.0.0.
• Need to upgrade to latest version in order to use best linting strategy for the code.
• Related to Support latest python versions #547 (review)

┆Issue is synchronized with this Jira Task by Unito

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➤ Automation for Jira commented:

The link to the corresponding Jira issue is https://ably.atlassian.net/browse/SDK-4040