bpo-36254: Fix invalid uses of %d in format strings in C. (GH-12264)

diff --git a/Modules/_io/winconsoleio.c b/Modules/_io/winconsoleio.c
index dd0997a..70a723e 100644
--- a/Modules/_io/winconsoleio.c
+++ b/Modules/_io/winconsoleio.c
@@ -725,7 +725,7 @@
 
     if (u8n) {
         PyErr_Format(PyExc_SystemError,
-            "Buffer had room for %d bytes but %d bytes required",
+            "Buffer had room for %zd bytes but %u bytes required",
             len, u8n);
         return -1;
     }