fix: Enable strict function checking

[kyleconroy]

Fixes #537

We need to add this behind a flag, otherwise it will break many people's build. To enable this, set strict_function_checks to true.

{
	"version": "1",
	"packages": [
		{
			"name": "querytest",
			"path": "go",
			"schema": "query.sql",
			"queries": "query.sql",
			"engine": "postgresql",
			"strict_function_checks": true
		}
	]
}