Bump dnspython from 2.3.0 to 2.4.2 (#2123)

* Bump dnspython from 2.3.0 to 2.4.2

Bumps [dnspython](https://github.com/rthalley/dnspython) from 2.3.0 to 2.4.2.
- [Release notes](https://github.com/rthalley/dnspython/releases)
- [Changelog](https://github.com/rthalley/dnspython/blob/master/doc/whatsnew.rst)
- [Commits](https://github.com/rthalley/dnspython/compare/v2.3.0...v2.4.2)

---
updated-dependencies:
- dependency-name: dnspython
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

* Update dnspython==2.4.2

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: JonnyWong16 <9099342+JonnyWong16@users.noreply.github.com>

[skip ci]

lib/dns/_asyncbackend.py

@@ -35,6 +35,9 @@ class Socket:  # pragma: no cover
     async def getsockname(self):
         raise NotImplementedError
 
+    async def getpeercert(self, timeout):
+        raise NotImplementedError
+
     async def __aenter__(self):
         return self
 
@@ -61,6 +64,11 @@ class StreamSocket(Socket):  # pragma: no cover
         raise NotImplementedError
 
 
+class NullTransport:
+    async def connect_tcp(self, host, port, timeout, local_address):
+        raise NotImplementedError
+
+
 class Backend:  # pragma: no cover
     def name(self):
         return "unknown"
@@ -83,3 +91,9 @@ class Backend:  # pragma: no cover
 
     async def sleep(self, interval):
         raise NotImplementedError
+
+    def get_transport_class(self):
+        raise NotImplementedError
+
+    async def wait_for(self, awaitable, timeout):
+        raise NotImplementedError