Update spec version in docs

[bollwyvl]

References

• remembered while responding to Metals (scala language server) integration with jupyterlab-lsp #407
• includes the smallest atest fix from investigate escaping jumping to definition (and other features) with spaces #406 to get CI working

Code changes

• check whether a diagnostic canary 🐦 is contained within the title when re-configuring, rather than starts with

User-facing changes

• Docs are (more) accurate, showing schema version 2 instead of 1

Backwards-incompatible changes

N/A

Chores

• linted
• tested
• documented
• changelog entry