adjust typeCast type in MySqlConnectionConfig (#20431)

The underlying node-mysql package supports a function as typeCast value (alternative to a boolean), thus its type has been set to any in the respective types package (@types/mysql). https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/mysql/index.d.ts#L217

types/knex/index.d.ts

@@ -563,7 +563,7 @@ declare namespace Knex {
         connectTimeout?: number;
         stringifyObjects?: boolean;
         insecureAuth?: boolean;
-        typeCast?: boolean;
+        typeCast?: any;
         queryFormat?: (query: string, values: any) => string;
         supportBigNumbers?: boolean;
         bigNumberStrings?: boolean;