[CI] Disable cSpell inside code blocks for mermaid, and others?

[chalin]

This was inspired by work on #3651. There are too many false positives in running cSpell over mermaid code blocks, but I'm starting to think that we might want to disable spelling checks for all code blocks. WDYT @open-telemetry/docs-maintainers?

[theletterf]

Wholeheartedly agree on disabling spell checks for code blocks. The only risk I see is getting typos in code comments, but I'm not that concerned about it if the net outcome is lowering friction for contributors.