[3.7] bpo-36254: Fix invalid uses of %d in format strings in C. (GH-12264). (GH-12322)

(cherry picked from commit d53fe5f407ff4b529628b01a1bcbf21a6aad5c3a)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Modules/_ssl.c b/Modules/_ssl.c
index 9baec8a..7076fdd 100644
--- a/Modules/_ssl.c
+++ b/Modules/_ssl.c
@@ -3348,7 +3348,7 @@
 #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;
     }