Logging flow chart missing from PDF

[bessman]

Documentation

gh-121035 changed the format of the logging HOWTO flow chart from PNG to SVG. This broke the inclusion of the flow chart in the PDF doc build.

Linked PRs

• gh-123463: Include logging_flow.png in PDF docs #123464
• [3.13] gh-123463: Include logging_flow diagram in non-HTML docs (GH-123464) #123666
• [3.12] gh-123463: Include logging_flow diagram in non-HTML docs (GH-123464) #123667