fix(apple): Add mention of refactoring fo SentryDsn (#15781)

Author: philprime

docs/platforms/apple/common/migration/index.mdx

@@ -103,6 +103,7 @@ For more information, see the <PlatformLink to="/profiling/#enable-ui-profiling"
 - The `function` property on `SentryFrame` now defaults to `nil` instead of `"<redacted>"`
 - The `value` and `type` properties on `SentryException` are now nullable; when `NSException` has no reason, `type` is set to `nil`
 - We changed the type of the `http.response.status_code` attribute for spans to int
+- We converted `SentryDsn` to Swift and removed the public header file `SentryDsn.h`
 
 #### Renamed APIs