Discourse's canonical url not being used for topic embeddings

Discourse is an open source discussion platform. Prior to version 3.0.4 of the `stable` branch and version 3.1.0.beta5 of the `beta` and `tests-passed` branches, multiple duplicate topics could be created if topic embedding is enabled. This issue is patched in version 3.0.4 of the `stable` branch and version 3.1.0.beta5 of the `beta` and `tests-passed` branches. As a workaround, disable topic embedding if it has been enabled.