fix(scanner): do not allow whitespaces in dollar quote tag

[eklmv]

Whitespace characters not allowed in dollar quoted tags. docs:

The tag, if any, of a dollar-quoted string follows the same rules as an unquoted identifier, except that it cannot contain a dollar sign.

Fixes problems with sqlc queries, which use positional parameters outside function definitions or prepared statements. For example:

SELECT * FROM a
LIMIT $1 OFFSET $2;

SELECT * FROM b
LIMIT $1 OFFSET $2;

$1 OFFSET $ should not be recognized as a tag name.