call PyErr_Clear() when ignoring error from PyNumber_Int (closes #15516)

Patch from Tom Tromey.
diff --git a/Misc/NEWS b/Misc/NEWS
index 5e719e5..45a4979 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -9,6 +9,9 @@
 Core and Builtins
 -----------------
 
+- Issue #15516: Fix a bug in PyString_FromFormat where it failed to properly
+  ignore errors from a __int__() method.
+
 - Issue #16839: Fix a segfault when calling unicode() on a classic class early
   in interpreter initialization.