fix: build on ubuntu-20.04 to ensure compatibility

[maxirmx]

No description provided.

[ronaldtse]

I believe this will fix:

• Use bundler in GHA builds metanorma/bipm-si-brochure#277

[maxirmx]

@CAMOBAP @ronaldtse
Seesking help .... Why rake for metanorma fails like in this run https://github.com/fontist/ffi-libarchive-binary/actions/runs/12444447089/job/34744929504 ? Is it something related to libarchive ?

Thank you

[CAMOBAP]

@maxirmx to b on the same page in https://github.com/fontist/ffi-libarchive-binary/actions/runs/12444447089/job/34744929504 where exactly it fails? All jobs look green

[maxirmx]

@maxirmx to b on the same page in https://github.com/fontist/ffi-libarchive-binary/actions/runs/12444447089/job/34744929504 where exactly it fails? All jobs look green

In "metanorma" jobs it fails on "bundle exec rake"
I set contineue-on-failure: true to be able test container
Sorry for confusion

[maxirmx]

The same issue with other gems
https://github.com/fontist/fontist/actions/runs/12446693626/job/34749370945?pr=390
so I assume it is not related to my changes