DATE parsing of image name in test job not working

The parsing of DATE in nightlies isn't working for the image name for the test job.

See this line: https://gitlab.cern.ch/avendras/otsdocker/-/blob/9e9a2b2c175583e9d2cb02439ea4e4812edb7d7d/.gitlab-ci.yml#L145

Leads to problems like this: https://gitlab.cern.ch/avendras/otsdocker/-/jobs/41779104

Discussed in avendras/otsdocker#69 (closed)

Plan: Let's turn off the test job for nightlies for now. And someone takes care of fixing this in parallel.