bpo-34217: Use lowercase for windows headers (GH-8472)

(cherry picked from commit e6a4755e6793942b950c1595e0c34bd66a0ee13e)

Co-authored-by: Erik Janssens <erik.janssens@conceptive.be>
diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 6674465..0d8a638 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -21,7 +21,7 @@
 #endif /* HAVE_SYS_STAT_H */
 
 #ifdef MS_WINDOWS
-#include <Windows.h>
+#include <windows.h>
 #endif
 
 /* Various interned strings */
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index c264d33..ea01a28 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -303,7 +303,7 @@
 # endif
 
 /* Provides the IsWindows7SP1OrGreater() function */
-#include <VersionHelpers.h>
+#include <versionhelpers.h>
 
 /* remove some flags on older version Windows during run-time.
    https://msdn.microsoft.com/en-us/library/windows/desktop/ms738596.aspx */