Fix the infamous ENOENT for /opt/gitlab/licenses/registry.csv

Until now, every few builds failed with ENOENT for the (apparently)
just copied /opt/gitlab/licenses/registry.csv

I finally went through the lengthy steps to reproduce, using an
actual cache zip from S3, and it turns
out that the ENOENT is due to the missing parent directory.

This never happens without the cache, probably because
an earlier step that creates this directory gets then always executed.

Ensuring the directory before hand as done in the CI configuration
was enough to fix the problem on the reproduction setup, but not in
CI, but the `mkdir` from `registry.rb` did fix it. We're keeping the
former one in case it would help with other cases of licenses aggregation.

--HG--
branch : heptapod-stable
4 jobs for !58 with topic/heptapod-stable/license-pbm in 46 minutes and 5 seconds (queued for 3 seconds)
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