use explicit typing for lexer lookahead

[the-mikedavis]

Checklist: ✅

• All tests pass in CI
• There are sufficient tests for the new fix/feature (N/A)
• Grammar rules have not been renamed unless absolutely necessary (0 rules renamed)
• The conflicts section hasn't grown too much (0 new conflicts)
• The parser size hasn't grown too much (master: 2330, PR: 2330)

👋 hello!

The auto typing is problematic for older c++ toolchains. In my case, it fails to cross-compile from x86_64-linux to aarch64-linux because of an old compiler. Declaring the type explicitly works fine though. What do you think?

[patrickt]

LGTM.