CondaKeyError in master pipelines

@duncanmmacleod Pipelines on MRs seem to be working again, but after merging to master the lalpulsar:conda and lalburst:conda jobs sometimes fail with

CondaKeyError: 'aggressive_update_packages': 'openssl' is not in the 'aggressive_update_packages' key of the config file

e.g. here and here. (Between these two, another one seems to have worked.)

Note that a little bit further up the output there's also a DuplicateKeyFutureWarnin that might be worth a look.