[doc] fix broken link in form-recognizer CHANGELOG (Azure#26791)

resolves Azure#26789

sdk/formrecognizer/ai-form-recognizer/CHANGELOG.md

@@ -183,7 +183,7 @@ From the last beta release (4.1.0-beta.1):
 
 ## 4.0.0-beta.1 (2021-10-07)
 
-This new major version beta introduces a full redesign of the Azure Form Recognizer client library. To leverage features of the newest Form Recognizer service API (version "2021-09-30-preview" and newer), the new SDK is required, and application code must be changed to use the new clients. Please see the [Migration Guide](https://github.com/azure/azure-sdk-for-js/blob/main/sdk/formrecognizer/ai-form-recognizer/MIGRATION-v3_v4.md) for detailed instructions on how to update application code from version 3.x of the Form Recognizer SDK to the new version (4.x). The following sections contain an outline of the changes.
+This new major version beta introduces a full redesign of the Azure Form Recognizer client library. To leverage features of the newest Form Recognizer service API (version "2021-09-30-preview" and newer), the new SDK is required, and application code must be changed to use the new clients. Please see the [Migration Guide](https://github.com/Azure/azure-sdk-for-js/blob/09eeb926e5c632ec27b386b47adb33f1a893aeb6/sdk/formrecognizer/ai-form-recognizer/MIGRATION-v3_v4.md) for detailed instructions on how to update application code from version 3.x of the Form Recognizer SDK to the new version (4.x). The following sections contain an outline of the changes.
 
 ### Breaking Changes
 
@@ -203,7 +203,7 @@ This new major version beta introduces a full redesign of the Azure Form Recogni
   - Custom models no longer have a name that is distinct from the model ID (more accurately, the model ID and name have been unified).
   - You must now specify a model ID to create a model (whether composed, copied, or built). Previously, the Form Recognizer service would generate a GUID for the newly-created model. Now, the model ID may be any text (so long as it does not start with "prebuilt-"), and it must be provided when the model is created.
   - The `ModelInfo` type (previously `CustomFormModelInfo`) has been redesigned. It no longer contains `trainingDocuments`, and it has a property called `docTypes` that contains the information previously contained in `submodels`, but with a different shape. Please refer to the documentation for more information, as this type has changed significantly.
-- The structure of many output types has changed. The full list of changes is extensive and discussed in depth in [the migration guide](https://github.com/azure/azure-sdk-for-js/blob/main/sdk/formrecognizer/ai-form-recognizer/MIGRATION-v3_v4.md). The following are some of the changes:
+- The structure of many output types has changed. The full list of changes is extensive and discussed in depth in [the migration guide](https://github.com/Azure/azure-sdk-for-js/blob/09eeb926e5c632ec27b386b47adb33f1a893aeb6/sdk/formrecognizer/ai-form-recognizer/MIGRATION-v3_v4.md). The following are some of the changes:
   - When analyzing a document, the output is no longer an array of `RecognizedForm`s. All analysis methods—including custom/prebuilt model analysis, layout, and the generic document model—produce an `AnalyzeResult` or a subset thereof. The `AnalyzeResult` has fields for `pages`, `tables`, `styles`, `entities`, `keyValuePairs`, and `documents`. The `beginExtractLayout` and `beginExtractGenericDocument` methods produce subtypes (`LayoutResult` and `GenericDocumentResult` respectively) of `AnalyzeResult` that contain only those fields that are produced by that model. The list of changes within these types is extensive, as they have been redesigned. Please consult the documentation for more information.
   - The new type `AnalyzedDocument` replaces `RecognizedForm`. It does not contain a `pages` property, as `pages` are now a top-level property of the `AnalyzeResult`.
   - The new type `DocumentPage` replaces `FormPage`. It does not have a `tables` property, as `tables` are now a top-level property of the `AnalyzeResult`.