print/latex-biber: Downgrade to 2.19

In some scenarios, v2.20 did not work sufficiently with biblatex v3.19.
As recommended, switch back to v2.19. Therefore, partial revert of the
commit 59b78e28ea9fda5ca133ff448b82146191fbf91f.

Retained from the previous commit:

• Textual corrections to the port
• Pet portlint by rearranging Makefile entries
• Keeping the customizations for test environment

Reported by: Clemens Heitzinger (via private mail)

MFH: 2024Q4