Planbuilder: Traces do not record parse exceptions correctly

[kylebrandt]

The exception message in a trace ends up being a memory address instead of the message:

exception.message	
"{0xc006f85d80}"

exception.type	
"github.com/dolthub/go-mysql-server/sql/planbuilder.parseErr"

I believe this is because the span method on the sql.Context needs parseErr to implement Error (have the Error() string method). Since this is missing we get an address instead.

[elianddb]

@kylebrandt implemented the fix you suggested (#3147), however, to help fully validate could you share more details about your setup. You can also test it with the PR if not possible.