Upgrade pg_query_go to v6

[ankane]

Hi, thanks for BemiDB!

Building on macOS 15.5 currently fails with:

# github.com/pganalyze/pg_query_go/v5/parser
src_port_snprintf.c:374:1: error: static declaration of 'strchrnul' follows non-static declaration
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_string.h:198:9: note: previous declaration is here
src_port_snprintf.c:438:27: warning: 'strchrnul' is only available on macOS 15.4 or newer [-Wunguarded-availability-new]
/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/_string.h:198:9: note: 'strchrnul' has been marked as being introduced in macOS 15.4 here, but the deployment target is macOS 15.0.0
src_port_snprintf.c:438:27: note: enclose 'strchrnul' in a __builtin_available check to silence this warning

This is fixed in pg_query_go v6.1.0: pganalyze/pg_query_go#132

[exAspArk]

Thank you for submitting the PR, @ankane! 🎉

P.S. I'm a big fan of your Ruby gems ❤️

[ankane]

No problem, thanks @exAspArk!