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

diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index 0e720e2..f2ce7fa 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -3347,7 +3347,7 @@
 #if HAVE_ALPN
     if ((size_t)protos->len > UINT_MAX) {
         PyErr_Format(PyExc_OverflowError,
-            "protocols longer than %d bytes", UINT_MAX);
+            "protocols longer than %u bytes", UINT_MAX);
         return NULL;
     }