Merge #21371: fuzz: fix gcc Woverloaded-virtual build warnings

36aa295 fuzz: fix gcc Woverloaded-virtual build warnings (Jon Atack)

Pull request description:

  Possible fixup to gcc build warnings since merge of b22d4c1. Closes #21369.

ACKs for top commit:
  practicalswift:
    cr ACK 36aa295: patch looks correct
  achow101:
    ACK 36aa295
  kristapsk:
    ACK 36aa295, this fixes compiler warnings for me with GCC 9.3.0.

Tree-SHA512: b6c99690ff72b809ce8105696744546252691b618f54311a9d930d9975fc692071ef408450f618fbb4aa99ee5390028a6eabbc968e22b2e8d2bd56bbafef49f8

src/test/fuzz/util.h

@@ -543,6 +543,12 @@ class FuzzedSock : public Sock
     {
     }
 
+    FuzzedSock& operator=(Sock&& other) override
+    {
+        assert(false && "Not implemented yet.");
+        return *this;
+    }
+
     SOCKET Get() const override
     {
         assert(false && "Not implemented yet.");