Remove the deprecated cgi module (#17741)

Removes all uses of the `cgi` module from Synapse. It was deprecated in
Python version 3.11 and removed in version 3.13 ([“dead
battery”](https://docs.python.org/3.13/whatsnew/3.13.html#pep-594-remove-dead-batteries-from-the-standard-library)).

### Pull Request Checklist

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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`.".
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@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: Quentin Gliech <quenting@element.io>

contrib/graph/graph.py

@@ -20,8 +20,8 @@
 #
 
 import argparse
-import cgi
 import datetime
+import html
 import json
 import urllib.request
 from typing import List
@@ -85,7 +85,7 @@ def make_graph(pdus: List[dict], filename_prefix: str) -> None:
             "name": name,
             "type": pdu.get("pdu_type"),
             "state_key": pdu.get("state_key"),
-            "content": cgi.escape(json.dumps(pdu.get("content")), quote=True),
+            "content": html.escape(json.dumps(pdu.get("content")), quote=True),
             "time": t,
             "depth": pdu.get("depth"),
         }