[TASK] CI: Use docker 20.10 instead of 19.03

Switching to 20.10 gives us a feature we need
in runTests.sh.

Resolves: #96013
Related: #94932
Related: #95999
Releases: master, 10.4
Change-Id: I7eef83c130b76cab84dff7d595b7807d34b22ce7
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72212


Tested-by: core-ci <typo3@b13.com>
Tested-by: Simon Gilli <typo3@gilbertsoft.org>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Simon Gilli <typo3@gilbertsoft.org>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>