Unskip SET with auto_increment validation tests

- Removed Skip: true from "set with auto increment" test
- Our validation now correctly handles SET columns with AUTO_INCREMENT
- All assertions expect "Incorrect column specifier" errors which match MySQL behavior
- Fixes issue dolthub/dolt#9470

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: elianddb

enginetest/queries/script_queries.go

@@ -9606,7 +9606,6 @@ where
 		},
 	},
 	{
-		Skip:    true,
 		Name:    "set with auto increment",
 		Dialect: "mysql",
 		SetUpScript: []string{