Fix support for older versions of zope-interface (#19274)

Fixes #19269 

Versions of zope-interface from RHEL, Ubuntu LTS 22 & 24 and OpenSuse
don't support the new python union `X | Y` syntax for interfaces. This
PR partially reverts the change over to fully use the new syntax, adds a
minimum supported version of zope-interface to Synapse's dependency
list, and removes the linter auto-upgrades which prefer the newer
syntax.

### Pull Request Checklist

<!-- Please read
https://element-hq.github.io/synapse/latest/development/contributing_guide.html
before submitting your pull request -->

* [X] Pull request is based on the develop branch
* [X] Pull request includes a [changelog
file](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#changelog).
The entry should:
- Be a short description of your change which makes sense to users.
"Fixed a bug that prevented receiving messages from other servers."
instead of "Moved X method from `EventStore` to `EventWorkerStore`.".
  - Use markdown where necessary, mostly for `code blocks`.
  - End with either a period (.) or an exclamation mark (!).
  - Start with a capital letter.
- Feel free to credit yourself, by adding a sentence "Contributed by
@github_username." or "Contributed by [Your Name]." to the end of the
entry.
* [X] [Code
style](https://element-hq.github.io/synapse/latest/code_style.html) is
correct (run the
[linters](https://element-hq.github.io/synapse/latest/development/contributing_guide.html#run-the-linters))

---------

Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>

tests/server.py

@@ -147,7 +147,7 @@ class FakeChannel:
     _reactor: MemoryReactorClock
     result: dict = attr.Factory(dict)
     _ip: str = "127.0.0.1"
-    _producer: IPullProducer | IPushProducer | None = None
+    _producer: Optional[Union[IPullProducer, IPushProducer]] = None
     resource_usage: ContextResourceUsage | None = None
     _request: Request | None = None
 
@@ -248,7 +248,7 @@ class FakeChannel:
         # TODO This should ensure that the IProducer is an IPushProducer or
         # IPullProducer, unfortunately twisted.protocols.basic.FileSender does
         # implement those, but doesn't declare it.
-        self._producer = cast(IPushProducer | IPullProducer, producer)
+        self._producer = cast(Union[IPushProducer, IPullProducer], producer)
         self.producerStreaming = streaming
 
         def _produce() -> None:
@@ -852,7 +852,7 @@ class FakeTransport:
     """Test reactor
     """
 
-    _protocol: IProtocol | None = None
+    _protocol: Optional[IProtocol] = None
     """The Protocol which is producing data for this transport. Optional, but if set
     will get called back for connectionLost() notifications etc.
     """
@@ -871,7 +871,7 @@ class FakeTransport:
     disconnected = False
     connected = True
     buffer: bytes = b""
-    producer: IPushProducer | None = None
+    producer: Optional[IPushProducer] = None
     autoflush: bool = True
 
     def getPeer(self) -> IPv4Address | IPv6Address:
@@ -1073,7 +1073,7 @@ def setup_test_homeserver(
     cleanup_func: Callable[[Callable[[], Optional["Deferred[None]"]]], None],
     server_name: str = "test",
     config: HomeServerConfig | None = None,
-    reactor: ISynapseReactor | None = None,
+    reactor: Optional[ISynapseReactor] = None,
     homeserver_to_use: type[HomeServer] = TestHomeServer,
     db_txn_limit: int | None = None,
     **extra_homeserver_attributes: Any,