Announced #28939 (`void f() => e` allows an e of any type) in changelog

CHANGELOG.md

 ## 1.24.0
 
 ### Language
 * During a dynamic type check, `void` is not required to be `null` anymore.
   In practice, this makes overriding `void` functions with non-`void` functions
   safer.
+* During static analysis, a function declared using `=>` with return type `void`
+  now allows the returned expression to have any type. For example, assuming the
+  declaration `int x;`, it is now type correct to have `void f() => ++x;`.
 
 #### Strong Mode
 
 * Removed ad hoc Future.then inference in favor of using FutureOr.  Prior to
 adding FutureOr to the language, the analyzer implented an ad hoc type inference
 for Future.then (and overrides) treating it as if the onValue callback was typed
 to return FutureOr for the purposes of inference.  This ad hoc inference has
 been removed now that FutureOr has been added.
 
 Packages that implement `Future` must either type the `onValue` parameter to
 `.then` as returning `FutureOr<T>`, or else must leave the type of the parameter
 entirely to allow inference to fill in the type.
 
+* The following is also a change in strong mode: During static analysis, a
+  function declared using `=>` with return type `void` now allows the returned
+  expression to have any type.
 
 ### Core library changes
 
 * `dart:io`
   * Added `Platform.localeName`, needed for accessing the locale on platforms
     that don't store it in an environment variable.
   * Added `ProcessInfo.currentRss` and `ProcessInfo.maxRss` for inspecting
     the Dart VM process current and peak resident set size.
   * Added 'RawSynchronousSocket', a basic synchronous socket implementation.
 * `dart:convert`
@@ skipping 1875 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.