fix(rds): serverlessV2MaxCapacity can be set to 0.5, which is invalid (…

…#32232)

### Issue # (if applicable)

N/A

### Reason for this change
In [CFn docs](https://docs.aws.amazon.com/ja_jp/AWSCloudFormation/latest/UserGuide/aws-properties-rds-dbcluster-serverlessv2scalingconfiguration.html#cfn-rds-dbcluster-serverlessv2scalingconfiguration-maxcapacity),  MaximumCapacity value must be higher than 0.5 ACUs.

```
The maximum capacity must be higher than 0.5 ACUs.
```

This means MaximumCapacity cannot be set to 0.5 ACUs. 
However, in the CDK, `serverlessV2MaxCapacity` can be set to 0.5, which is invalid.

When I attempted to deploy with `serverlessV2MaxCapacity` set to 0.5, I encountered the following error:
> CREATE_FAILED        | AWS::RDS::DBCluster                         | Integ-Cluster (IntegCluster4261F36F) Resource handler returned message: "Serverless v2 maximum capacity 0.5 isn't valid. The maximum capacity must be at least 1.0.

In the Management Console, Maximum Capacity cannot be set to 0.5.

<img width="854" alt="image" src="https://github.com/user-attachments/assets/37c127d8-cd5d-4e88-a699-dff7929a8b95">




### Description of changes
Fix a validation.



### Description of how you validated changes
Fix unit tests.


### 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*

packages/aws-cdk-lib/aws-rds/lib/cluster.ts

@@ -1074,8 +1074,8 @@ abstract class DatabaseClusterNew extends DatabaseClusterBase {
   }
 
   private validateServerlessScalingConfig(): void {
-    if (this.serverlessV2MaxCapacity > 256 || this.serverlessV2MaxCapacity < 0.5) {
-      throw new Error('serverlessV2MaxCapacity must be >= 0.5 & <= 256');
+    if (this.serverlessV2MaxCapacity > 256 || this.serverlessV2MaxCapacity < 1) {
+      throw new Error('serverlessV2MaxCapacity must be >= 1 & <= 256');
     }
 
     if (this.serverlessV2MinCapacity > 256 || this.serverlessV2MinCapacity < 0) {
@@ -1086,9 +1086,6 @@ abstract class DatabaseClusterNew extends DatabaseClusterBase {
       throw new Error('serverlessV2MaxCapacity must be greater than serverlessV2MinCapacity');
     }
 
-    if (this.serverlessV2MaxCapacity === 0.5 && this.serverlessV2MinCapacity === 0.5) {
-      throw new Error('If serverlessV2MinCapacity === 0.5 then serverlessV2MaxCapacity must be >=1');
-    }
     const regexp = new RegExp(/^[0-9]+\.?5?$/);
     if (!regexp.test(this.serverlessV2MaxCapacity.toString()) || !regexp.test(this.serverlessV2MinCapacity.toString())) {
       throw new Error('serverlessV2MinCapacity & serverlessV2MaxCapacity must be in 0.5 step increments, received '+

packages/aws-cdk-lib/aws-rds/test/cluster.test.ts

@@ -116,11 +116,10 @@ describe('cluster new api', () => {
     });
 
     test.each([
-      [0.5, 300, /serverlessV2MaxCapacity must be >= 0.5 & <= 256/],
-      [0.5, 0, /serverlessV2MaxCapacity must be >= 0.5 & <= 256/],
+      [0.5, 300, /serverlessV2MaxCapacity must be >= 1 & <= 256/],
+      [0.5, 0, /serverlessV2MaxCapacity must be >= 1 & <= 256/],
       [-1, 1, /serverlessV2MinCapacity must be >= 0 & <= 256/],
       [300, 1, /serverlessV2MinCapacity must be >= 0 & <= 256/],
-      [0.5, 0.5, /If serverlessV2MinCapacity === 0.5 then serverlessV2MaxCapacity must be >=1/],
       [10.1, 12, /serverlessV2MinCapacity & serverlessV2MaxCapacity must be in 0.5 step increments/],
       [12, 12.1, /serverlessV2MinCapacity & serverlessV2MaxCapacity must be in 0.5 step increments/],
       [5, 1, /serverlessV2MaxCapacity must be greater than serverlessV2MinCapacity/],