Fix tests on Twisted trunk. (#16528)

Twisted trunk makes a change to the `TLSMemoryBIOFactory` where
the underlying protocol is changed from `TLSMemoryBIOProtocol` to
`BufferingTLSTransport` to improve performance of TLS code (see
https://github.com/twisted/twisted/issues/11989).

In order to properly hook this code up in tests we need to pass the test
reactor's clock into `TLSMemoryBIOFactory` to avoid the global (trial)
reactor being used by default.

Twisted does something similar internally for tests:
157cd8e659/src/twisted/web/test/test_agent.py (L871-L874)

tests/server.py

@@ -43,9 +43,11 @@ from typing import (
 from unittest.mock import Mock
 
 import attr
+from incremental import Version
 from typing_extensions import ParamSpec
 from zope.interface import implementer
 
+import twisted
 from twisted.internet import address, tcp, threads, udp
 from twisted.internet._resolver import SimpleResolverComplexifier
 from twisted.internet.defer import Deferred, fail, maybeDeferred, succeed
@@ -474,6 +476,16 @@ class ThreadedMemoryReactorClock(MemoryReactorClock):
                     return fail(DNSLookupError("OH NO: unknown %s" % (name,)))
                 return succeed(lookups[name])
 
+        # In order for the TLS protocol tests to work, modify _get_default_clock
+        # on newer Twisted versions to use the test reactor's clock.
+        #
+        # This is *super* dirty since it is never undone and relies on the next
+        # test to overwrite it.
+        if twisted.version > Version("Twisted", 23, 8, 0):
+            from twisted.protocols import tls
+
+            tls._get_default_clock = lambda: self  # type: ignore[attr-defined]
+
         self.nameResolver = SimpleResolverComplexifier(FakeResolver())
         super().__init__()