Add missing include for crtdbg.h (#4534)

This header uses _CRT_ASSERT, which is defined in crtdbg.h but does not
include it, causing a build error in format-test.cc

Fixes the issue by including the header

test/gtest-extra.h

@@ -15,6 +15,10 @@
 #include "fmt/os.h"
 #include "gmock/gmock.h"
 
+#ifdef _MSC_VER
+#  include <crtdbg.h>
+#endif
+
 #define FMT_TEST_THROW_(statement, expected_exception, expected_message, fail) \
   GTEST_AMBIGUOUS_ELSE_BLOCKER_                                                \
   if (::testing::AssertionResult gtest_ar = ::testing::AssertionSuccess()) {   \