h3 uppercase_name does not recognize "A AA" as a headline

[justinmk]

Problem

reported by @ychin neovim/neovim#20690 (comment) :

minor bug in the tree-sitter parser logic where a single character (e.g. "A" in "STARTING MACVIM FROM A TERMINAL") does not count as a headline. ... grammar.json ... requires two or more characters: [A-Z0-9.()][-A-Z0-9.()_]+.