Bump tree-sitter version to 0.20

[hendrikvanantwerpen]

Checklist:

• All tests pass in CI.
• There are sufficient tests for the new fix/feature.
• Grammar rules have not been renamed unless absolutely necessary.
• The conflicts section hasn't grown too much.
• The parser size hasn't grown too much (check the value of STATE_COUNT in src/parser.c).

[aibaars]

This change is already present in the recently merged f0995f0

[aibaars]

Looks good to me. I double-checked that running npx tree-sitter-cli generate does not change the generated code.

[hendrikvanantwerpen]

Thanks for verifying that, @aibaars! I found that any CLI devDependencies are on the PATH for the scripts in package.json that are run via npm run, and using npx explicitly is not necessary.