Add OpenJDK as a dependency again

[deeplow]

The removal of openjdk in #305 introduced some unintended side-effects of removing openjdk8 in excell files:

before	after

We missed these because we didn't manually inspect all the output files and also because the conversion process dones't fail as soon as it gets an unexpected JSON from container:

Converting document to safe PDF
[DEBUG] Marking doc GQN_Qw as 'converting'
[INFO ] > /usr/bin/podman run --network none -u dangerzone --security-opt no-new-privileges --userns keep-id --cap-drop all --rm -v /home/user/dangerzone/tests/test_docs/sample.xlsx:/tmp/input_file -v /home/user/.config/dangerzone/tmp/tmpphanvmpz/pixels:/dangerzone dangerzone.rocks/dangerzone /usr/bin/python3 /usr/local/bin/dangerzone.py document-to-pixels
[INFO ] [doc GQN_Qw] 0% Converting to PDF using LibreOffice
[ERROR] Invalid JSON returned from container:

	 javaldx: Could not find a Java Runtime Environment!

[ERROR] Invalid JSON returned from container:

	 Warning: failed to read path from javaldx

[ERROR] Invalid JSON returned from container:

	 convert /tmp/input_file -> /tmp/input_file.pdf using filter : calc_pdf_Export

[INFO ] [doc GQN_Qw] 3% Calculating number of pages
[INFO ] [doc GQN_Qw] 10% Converting page 1/6 to pixels
[INFO ] [doc GQN_Qw] 18% Converting page 2/6 to pixels
[INFO ] [doc GQN_Qw] 25% Converting page 3/6 to pixels
[INFO ] [doc GQN_Qw] 33% Converting page 4/6 to pixels
[INFO ] [doc GQN_Qw] 40% Converting page 5/6 to pixels
[INFO ] [doc GQN_Qw] 48% Converting page 6/6 to pixels

It needs to be reverted. And out tests should at least include some sort of diff so things like these get flagged.