chore: fix spelling error of if (#31353)

I saw this while reading the [EC2 instance docs](https://docs.aws.amazon.com/cdk/api/v2/docs/aws-cdk-lib.aws_ec2.Instance.html#userdatacausesreplacement).

Author: msambol

packages/@aws-cdk/cloudformation-diff/lib/diff-template.ts

@@ -151,7 +151,7 @@ function calculateTemplateDiff(currentTemplate: { [key: string]: any }, newTempl
 /**
  * Replace all references to the given logicalID on the given template, in-place
  *
- * Returns true iff any references were replaced.
+ * Returns true if any references were replaced.
  */
 function propagateReplacedReferences(template: object, logicalId: string): boolean {
   let ret = false;

packages/aws-cdk-lib/aws-ec2/lib/instance.ts

@@ -177,7 +177,7 @@ export interface InstanceProps {
    * UserData, which will cause CloudFormation to replace it if the UserData
    * changes.
    *
-   * @default - true iff `initOptions` is specified, false otherwise.
+   * @default - true if `initOptions` is specified, false otherwise.
    */
   readonly userDataCausesReplacement?: boolean;
 

packages/aws-cdk/lib/notices.ts

@@ -255,7 +255,7 @@ export class NoticeFilter {
   }
 
   /**
-   * Returns true iff we should show this notice.
+   * Returns true if we should show this notice.
    */
   apply(notice: Notice): boolean {
     if (this.acknowledgedIssueNumbers.has(notice.issueNumber)) {
@@ -267,7 +267,7 @@ export class NoticeFilter {
   }
 
   /**
-   * Returns true iff we should show the notice.
+   * Returns true if we should show the notice.
    */
   private applyVersion(notice: Notice, name: string, compareToVersion: string | undefined) {
     if (compareToVersion === undefined) { return false; }