Note LoggingContext signature change incompatibility in 1.32.0 (#9859)

1.32.0 also introduced an incompatibility with Synapse modules that make use of `synapse.logging.context.LoggingContext`, such as [synapse-s3-storage-provider](https://github.com/matrix-org/synapse-s3-storage-provider).

This PR adds a note to the 1.32.0 changelog and upgrade notes about it.