https://ftp.acc.umu.se/mirror/wikimedia.org/dumps/enwiki/20190901/ doesn't exist

[unhammer]

referenced in data/download-ex-data-for-benchmarks.sh

[ocramz]

https://mirror.accum.se/mirror/wikimedia.org/dumps/enwiki/

Seems like they got rid of old data dumps. Good on them but perhaps we should host the file here in git-lfs