fix(types): Fix incorrect sampled type on Transaction (#11146)

`@sentry/types` does not align with `@sentry/core`, and it causes build
errors when `exactOptionalPropertyTypes` is `true`.

This patch fixes the type error by explicitly specifying `undefined`.

Author: quisido

packages/types/src/transaction.ts

@@ -66,7 +66,7 @@ export interface Transaction extends TransactionContext, Omit<Span, 'setName' |
    * Was this transaction chosen to be sent as part of the sample?
    * @deprecated Use `spanIsSampled(transaction)` instead.
    */
-  sampled?: boolean;
+  sampled?: boolean | undefined;
 
   /**
    * @inheritDoc