Use 'blocklist' instead of 'blacklist'

The word 'blacklist' comes from the medieval term 'black book'. However,
since 'black' is now used to describe people we should avoid additional
negative associations with it. Use 'blocklist'.

See also: https://www.zdnet.com/article/github-to-replace-master-with-alternative-term-to-avoid-slavery-references/
3 jobs for sam/tracker-miners-2.3-blocklist in 3 minutes and 10 seconds (queued for 1 second)
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