A number of tests are currently marked shard_split_incompatible (such as dbcase) because they use sibling databases, which will not work with the inject_tenant_prefix hook when multiple tenants are used for an operation. Now that shard merge uses multiple tenants we must also skip these tests when running shard merge passthroughs. One option is to mark them all incompatible_with_shard_merge, another option is to introduce a new tag incompatible_with_multiple_tenants and exclude that tag in the shard merge and shard split passthrough definitions.