Fix removed link (Azure#43363)

Just updated the dead link to point to the PR that remove the tool dotnet/arcade#14328.

At some point we will want to move to the new tool which is tracked at Azure#33433

CONTRIBUTING.md

@@ -249,7 +249,7 @@ dotnet build eng\service.proj /p:ServiceDirectory=eventhub /p:UpdateSourceOnBuil
 
 ## API Compatibility Verification
 
-.NET is using the [ApiCompat tool](https://github.com/dotnet/arcade/tree/main/src/Microsoft.DotNet.ApiCompat) to enforce API compatibility between versions. Builds of GA'ed libraries will fail locally and in CI if there are breaking changes.
+.NET is using the [ApiCompat tool](https://github.com/dotnet/arcade/pull/14328) to enforce API compatibility between versions. Builds of GA'ed libraries will fail locally and in CI if there are breaking changes.
 
 ### How it works
 Each library needs to provide a `ApiCompatVersion` property which is set to the last GA'ed version of the library that will be used to compare APIs with the current to ensure no breaks have been introduced. Projects with this property set will download the specified package and the ApiCompat (Microsoft.DotNet.ApiCompat) tools package as part of the restore step of the project. Then as a post build step of the project it will run ApiCompat to verify the current APIs are compatible with the last GA'ed version of the APIs. For libraries that wish to disable the APICompat check they can remove the `ApiCompatVersion` property from their project. Our version bump automation will automatically add or increment the `ApiCompatVersion` property to the project when it detects that the version it is changing was a GA version which usually indicates that we just shipped that GA version and so it should be the new baseline for API checks.