Documentation build broken due to pandoc+mermaid-filter

[remi-delmas-3000]

I've noticed that the Publish documentation workflow has been failing consistently for a while

https://github.com/diffblue/cbmc/actions/workflows/publish.yaml

The stage that fails is "Rendering mermaid diagrams", possibly due to pandoc+mermaid-filter. I was not able to reproduce the failure under macOS X v15.x.

Rendering mermaid diagrams
./architectural/central-data-structures.md
Error running filter mermaid-filter:
Error in $.blocks[6]: mempty
make: *** [Makefile:4: markdown] Error 83

CBMC version: 6.x
Operating system: CI build system ubuntu 22.04
Exact command line resulting in the issue: action triggered by PR
What behaviour did you expect: success
What happened instead: failure