Migrate to absl::AnyInvocable

PiperOrigin-RevId: 501392167

internal/platform/settable_future.h

@@ -16,6 +16,7 @@
 #define PLATFORM_PUBLIC_SETTABLE_FUTURE_H_
 
 #include <utility>
+#include <vector>
 
 #include "internal/platform/condition_variable.h"
 #include "internal/platform/mutex.h"
@@ -115,7 +116,7 @@ class SettableFuture : public api::SettableFuture<T> {
 
   mutable Mutex mutex_;
   ConditionVariable completed_{&mutex_};
-  std::vector<std::pair<api::Executor*, std::function<void()>>> listeners_;
+  std::vector<std::pair<api::Executor*, Runnable>> listeners_;
   bool done_{false};
   T value_;
   Exception exception_{Exception::kFailed};