folly: fixup AsyncTimeoutTest on windows

Summary:
In D14702587 I made a change to workaround an ICE in gcc 8.
It turns out to be a gift that keeps giving; with the code as-is
on windows we now encounter:

```
folly\io\async\test\AsyncTimeoutTest.cpp(29): error C3493: 'expected' cannot be implicitly captured because no default capture mode has been specified
```

Adding `expected` to the capture list yields this error with gcc, either with or without the reference:

```
stderr: folly/io/async/test/AsyncTimeoutTest.cpp:29:45: error: lambda capture 'expected' is not required to be captured for this use [-Werror,-Wunused-lambda-capture]
      AsyncTimeout::make(manager, [&value, &expected]() noexcept { value = expected; });
                                         ~~~^~~~~~~~
1 error generated.
```

the solution is to make `expected` not be `const`.

Reviewed By: yfeldblum

Differential Revision: D14721418

fbshipit-source-id: b65c17414c161b9dee7f269b2e2a22a980766a6c

folly/io/async/test/AsyncTimeoutTest.cpp

@@ -22,11 +22,11 @@ namespace folly {
 
 TEST(AsyncTimeout, make) {
   int value = 0;
-  int const expected = 10;
+  int expected = 10;
   EventBase manager;
 
-  auto observer =
-      AsyncTimeout::make(manager, [&value]() noexcept { value = expected; });
+  auto observer = AsyncTimeout::make(
+      manager, [&value, expected ]() noexcept { value = expected; });
 
   observer->scheduleTimeout(std::chrono::milliseconds(100));
 
@@ -37,11 +37,11 @@ TEST(AsyncTimeout, make) {
 
 TEST(AsyncTimeout, schedule) {
   int value = 0;
-  int const expected = 10;
+  int expected = 10;
   EventBase manager;
 
   auto observer = AsyncTimeout::schedule(
-      std::chrono::milliseconds(100), manager, [&value]() noexcept {
+      std::chrono::milliseconds(100), manager, [&value, expected ]() noexcept {
         value = expected;
       });
 
@@ -52,11 +52,11 @@ TEST(AsyncTimeout, schedule) {
 
 TEST(AsyncTimeout, schedule_immediate) {
   int value = 0;
-  int const expected = 10;
+  int expected = 10;
   EventBase manager;
 
   auto observer = AsyncTimeout::schedule(
-      std::chrono::milliseconds(0), manager, [&value]() noexcept {
+      std::chrono::milliseconds(0), manager, [&value, expected ]() noexcept {
         value = expected;
       });
 
@@ -66,11 +66,11 @@ TEST(AsyncTimeout, schedule_immediate) {
 
 TEST(AsyncTimeout, cancel_make) {
   int value = 0;
-  int const expected = 10;
+  int expected = 10;
   EventBase manager;
 
-  auto observer =
-      AsyncTimeout::make(manager, [&value]() noexcept { value = expected; });
+  auto observer = AsyncTimeout::make(
+      manager, [&value, expected ]() noexcept { value = expected; });
 
   std::weak_ptr<RequestContext> rctx_weak_ptr;
 
@@ -92,7 +92,7 @@ TEST(AsyncTimeout, cancel_make) {
 
 TEST(AsyncTimeout, cancel_schedule) {
   int value = 0;
-  int const expected = 10;
+  int expected = 10;
   EventBase manager;
   std::unique_ptr<AsyncTimeout> observer;
   std::weak_ptr<RequestContext> rctx_weak_ptr;
@@ -102,9 +102,9 @@ TEST(AsyncTimeout, cancel_schedule) {
     rctx_weak_ptr = RequestContext::saveContext();
 
     observer = AsyncTimeout::schedule(
-        std::chrono::milliseconds(100), manager, [&value]() noexcept {
-          value = expected;
-        });
+        std::chrono::milliseconds(100),
+        manager,
+        [&value, expected ]() noexcept { value = expected; });
 
     observer->cancelTimeout();
   }