fix(lambda): fix typo in addPermission() warning message (#37365)

### Reason for this change

The warning message displayed by `addPermission()` when called on a Lambda Function with mismatched environments contains a typo: "this is is intentional" (duplicated "is").

### Description of changes

Fix `this is is intentional` → `this is intentional` in:
- `packages/aws-cdk-lib/aws-lambda/lib/function-base.ts` (source)
- `packages/aws-cdk-lib/aws-lambda/test/function.test.ts` (test assertion)

### Description of how you validated changes

Updated the corresponding test assertion to match the corrected message.

### 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)

Author: syukawa-gh

packages/aws-cdk-lib/aws-lambda/lib/function-base.ts

@@ -406,7 +406,7 @@ export abstract class FunctionBase extends Resource implements IFunction, ec2.IC
   public addPermission(id: string, permission: Permission) {
     if (!this.canCreatePermissions) {
       if (!this._skipPermissions) {
-        Annotations.of(this).addWarningV2('UnclearLambdaEnvironment', `addPermission() has no effect on a Lambda Function with region=${this.env.region}, account=${this.env.account}, in a Stack with region=${Stack.of(this).region}, account=${Stack.of(this).account}. Suppress this warning if this is is intentional, or pass sameEnvironment=true to fromFunctionAttributes() if you would like to add the permissions.`);
+        Annotations.of(this).addWarningV2('UnclearLambdaEnvironment', `addPermission() has no effect on a Lambda Function with region=${this.env.region}, account=${this.env.account}, in a Stack with region=${Stack.of(this).region}, account=${Stack.of(this).account}. Suppress this warning if this is intentional, or pass sameEnvironment=true to fromFunctionAttributes() if you would like to add the permissions.`);
       }
       return;
     }

packages/aws-cdk-lib/aws-lambda/test/function.test.ts

@@ -252,7 +252,7 @@ describe('function', () => {
 
       expect(getWarnings(app.synth())).toEqual([
         {
-          message: expect.stringMatching(/^addPermission\(\) has no effect on a Lambda Function with region=us-west-2, account=123456789012, in a Stack with region=\${Token\[AWS\.Region\.\d+]}, account=\${Token\[AWS\.AccountId\.\d+]}. Suppress this warning if this is is intentional, or pass sameEnvironment=true to fromFunctionAttributes\(\) if you would like to add the permissions\. \[ack: UnclearLambdaEnvironment]$/),
+          message: expect.stringMatching(/^addPermission\(\) has no effect on a Lambda Function with region=us-west-2, account=123456789012, in a Stack with region=\${Token\[AWS\.Region\.\d+]}, account=\${Token\[AWS\.AccountId\.\d+]}. Suppress this warning if this is intentional, or pass sameEnvironment=true to fromFunctionAttributes\(\) if you would like to add the permissions\. \[ack: UnclearLambdaEnvironment]$/),
           path: '/Default/Imported',
         },
       ]);