_content/doc: ensure database example code compiles

The CreateOrder example function fails to compile for two reasons:
   A helper function with wrong number of return values (want 2, got 1).
   A short variable declaration (:=) does not declare new variables.

This change resolves the compiler error, allowing the code to compile.

Fixes golang/go#50508

Change-Id: Ife07ae1490969ae67525b9171ab4fcd424409c1c
Reviewed-on: https://go-review.googlesource.com/c/website/+/376974
Reviewed-by: Heschi Kreinick <[email protected]>
Run-TryBot: Emmanuel Odeke <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

_content/doc/database/execute-transactions.md

@@ -114,7 +114,7 @@ func CreateOrder(ctx context.Context, albumID, quantity, custID int) (orderID in
 
 	// Create a helper function for preparing failure results.
 	fail := func(err error) (int64, error) {
-		return fmt.Errorf("CreateOrder: %v", err)
+		return 0, fmt.Errorf("CreateOrder: %v", err)
 	}
 
 	// Get a Tx for making transaction requests.
@@ -152,7 +152,7 @@ func CreateOrder(ctx context.Context, albumID, quantity, custID int) (orderID in
 		return fail(err)
 	}
 	// Get the ID of the order item just created.
-	orderID, err := result.LastInsertId()
+	orderID, err = result.LastInsertId()
 	if err != nil {
 		return fail(err)
 	}