bpo-34217: Use lowercase header for Windows (GH-8453)

(cherry picked from commit 6cf8255912c36fec6f87f62513034d0818f61390)

Co-authored-by: erikjanss <erik.janssens@conceptive.be>
diff --git a/PC/getpathp.c b/PC/getpathp.c
index 9382843..bc85b58 100644
--- a/PC/getpathp.c
+++ b/PC/getpathp.c
@@ -89,7 +89,7 @@
 #endif
 
 #include <windows.h>
-#include <Shlwapi.h>
+#include <shlwapi.h>
 
 #ifdef HAVE_SYS_TYPES_H
 #include <sys/types.h>