clientv3: do not treat Internal codes as halting

Fixes #6277

clientv3/client.go

@@ -295,7 +295,14 @@ func isHaltErr(ctx context.Context, err error) bool {
 	if err == nil {
 		return false
 	}
-	return grpc.Code(err) != codes.Unavailable
+	code := grpc.Code(err)
+	// Unavailable codes mean the system will be right back.
+	// (e.g., can't connect, lost leader)
+	// Treat Internal codes as if something failed, leaving the
+	// system in an inconsistent state, but retrying could make progress.
+	// (e.g., failed in middle of send, corrupted frame)
+	// TODO: are permanent Internal errors possible from grpc?
+	return code != codes.Unavailable && code != codes.Internal
 }
 
 func toErr(ctx context.Context, err error) error {