chore(deps): update mysql docker tag to v9

[renovate]

This PR contains the following updates:

Package	Update	Change
mysql	major	5.7.44 → 9.7.0

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[YOU54F]

I think it is time we probably remove mysql testing and references from this codebase and pact-broker-docker

see

• pact_broker/README.md

  Line 154 in deac70a

  * MySQL was supported for the native Ruby application until around 2021, but the official `pactfoundation/pact-broker` Docker image does not support it. New features will not be optimised for MySQL, and some new features may not even be supported on it (eg. the database clean feature).

mysql2 gem still installed in pact-broker-docker

https://github.com/pact-foundation/pact-broker-docker/blob/master/pact_broker/Gemfile#L6

recent issue for mysql2 user

#834

we see similar issues in our CI, although they are marked as pending. so don't affect the test suite