Celery: don't use a signal object, but a string instead (#12333)

I've started noticing this some days ago and today I tried to debug it a
little. I didn't find anything in our side, so I opened an issue at
django-structlog.

jrobichaud/django-structlog#870

However, it ended up being our fault, so I'm updating our code here to
avoid keep failing and log this line properly.

Author: humitos

readthedocs/core/utils/__init__.py

@@ -1,7 +1,6 @@
 """Common utility functions."""
 
 import re
-import signal
 
 import structlog
 from django.conf import settings
@@ -279,7 +278,7 @@ def cancel_build(build):
         build_task_id=build.task_id,
         terminate=terminate,
     )
-    app.control.revoke(build.task_id, signal=signal.SIGINT, terminate=terminate)
+    app.control.revoke(build.task_id, signal="SIGINT", terminate=terminate)
 
 
 def send_email_from_object(email: EmailMultiAlternatives | EmailMessage):

readthedocs/rtd_tests/tests/test_core_utils.py

@@ -1,5 +1,4 @@
 """Test core util functions."""
-import signal
 from unittest import mock
 
 import pytest
@@ -209,8 +208,8 @@ def test_trigger_max_concurrency_reached(self, update_docs, app):
         )
         app.control.revoke.assert_has_calls(
             [
-                mock.call("1", signal=signal.SIGINT, terminate=True),
-                mock.call("0", signal=signal.SIGINT, terminate=True),
+                mock.call("1", signal="SIGINT", terminate=True),
+                mock.call("0", signal="SIGINT", terminate=True),
             ]
         )