Automerge stops dependabot when branch is unmergable

When dependabot is configured to merge automatically the branches it creates, those branches can be merged automatically during the update process.

When this happens, the next branches that will be created won't be able to be merged automatically (as the previous dumps were merged), and gitlab refuses the merge by sending a 422 response.

This 422 response is not caught, which stops dependabot during the update process. This merge request add's the 422 and 409 catches, so that dependabot can continue the update properly.