[P.6] trivial: s/a/the/ (#2288)

While "a wrong number can be passed" makes sense (and there are perhaps
good philosophical reasons to prefer it), I believe that the more natural
way to say it in common English is "the wrong number can be passed"; thus,
this commit changes "a" to "the" in the comment of a code example.

Author: mfwitten

CppCoreGuidelines.md

@@ -767,7 +767,7 @@ We can of course pass the number of elements along with the pointer:
 
     void g2(int n)
     {
-        // bad: a wrong number of elements can be passed to f2()
+        // bad: the wrong number of elements can be passed to f2()
         f2(new int[n], n);
     }