[NR.6] trivial: s/goto_exit/goto exit/ (#2287)

The example intended:

    goto exit;

However, it was mistakenly written as:

    goto_exit;

CppCoreGuidelines.md

@@ -20889,7 +20889,7 @@ This technique is a pre-exception technique for RAII-like resource and error han
         // ...
         int* p = (int*) malloc(n);
         // ...
-        if (some_error) goto_exit;
+        if (some_error) goto exit;
         // ...
     exit:
         free(p);