Docs issues for offline pdf builds

[KrystalDelusion]

Link to page

https://yosyshq.readthedocs.io/projects/yosys/en/latest/getting_started/installation.html#targeted-architectures

Build number

No response

Issue

When I don't patch out badge svg references, running make ABCEXTERNAL=/bin/abc DOC_TARGET=latexpdf docs in the rpm build container (mock) results in this error:badge_err.log

The main "highlight" is a bunch of entries similar to this:

WARNING: Could not fetch remote image: https://github.com/YosysHQ/oss-cad-suite-build/actions/workflows/darwin-arm64.yml/badge.svg
[HTTPSConnectionPool(host='github.com', port=443): Max retries exceeded with
url: /YosysHQ/oss-cad-suite-build/actions/workflows/darwin-arm64.yml/badge.svg  (Caused by
NameResolutionError("<urllib3.connection.HTTPSConnection object at   0x7f53a3dd42d0>:
Failed to resolve 'github.com' ([Errno -3] Temporary failure   in name resolution)"))]

I might be missing some environment setting that would bypass badge downloading (or otherwise be doing something silly on my end :) ) but as of right now (commit b89bd02) I can't build the pdf manual unless I explicitly remove badge references.

Originally posted by @gsomlo in #4725 (comment)

Expected

make DOC_TARGET=latexpdf docs should pass (meaning, no warnings-as-errors) even in offline build environments.