Disable `SYNAPSE_TEST_PATCH_LOG_CONTEXTS` causing false negatives in tests

This issue has been migrated from [#12796](https://github.com/matrix-org/synapse/issues/12796).

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`SYNAPSE_TEST_PATCH_LOG_CONTEXTS` causes Synapse to monkey-patch `defer.inlineCallbacks` to add some checks that we handle logcontexts correctly. We enable it when running sytests (and possibly trial tests?)

The problem is that it is now causing false negatives (in particular, `txredisapi` also uses `inlineCallbacks`, and because it's not Synapse code, it fails the checks).

A better alternative might be to modify the places we use `defer.ensureDeferred` to do this wrapping instead. For now, we should probably just disable it.