docs(rds): fix typos (#32874)

### Issue # (if applicable)

None

### Reason for this change

Fixed typos in code comments.

### Checklist
- [x] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: andyu17

packages/aws-cdk-lib/aws-rds/lib/database-secret.ts

@@ -99,7 +99,7 @@ export class DatabaseSecret extends secretsmanager.Secret {
       const hash = md5hash(JSON.stringify({
         // Use here the options that influence the password generation.
         // If at some point we add other password customization options
-        // they sould be added here below (e.g. `passwordLength`).
+        // they should be added here below (e.g. `passwordLength`).
         excludeCharacters,
       }));
       const logicalId = `${Names.uniqueId(this)}${hash}`;