#19449: Handle non-string keys when generating 'fieldnames' error.

Backport from 3.3 6e5afeada7ca.
diff --git a/Misc/NEWS b/Misc/NEWS
index 77bc5a8..d5ed3c9 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,9 @@
 Library
 -------
 
+- Issue #19449: in csv's writerow, handle non-string keys when generating the
+  error message that certain keys are not in the 'fieldnames' list.
+
 - Issue #12853: Fix NameError in distutils.command.upload.
 
 - Issue #19523: Closed FileHandler leak which occurred when delay was set.