Fix another jsonschema typecheck error (#11830)

Similar to #11817.

In `_create_power_level_validator` we
- retrieve `validator`. This is a class implementing the
  `jsonschema.protocols.Validator` interface. In other words,
  `validator: Type[jsonschema.protocols.Validator]`.
- we then create an second validator class by modifying the original
  `validator`. We return that class, which is also of type
  `Type[jsonschema.protocols.Validator]`.

So the original annotation was incorrect: it claimed we were returning
an instance of jsonSchema.Draft7Validator, not the class (or a subclass)
itself. (Strictly speaking this is incorrect, because `POWER_LEVELS_SCHEMA`
isn't pinned to a particular version of JSON Schema. But there are other
complications with the type stubs if you try to fix this; I felt like
the change herein was a decent compromise that better expresses intent).

(I suspect/hope the typeshed project would welcome an effort to improve
the jsonschema stubs. Let's see if I get some spare time.)

1 files changed, 1 insertions, 0 deletions

diff --git a/changelog.d/11830.misc b/changelog.d/11830.misc
new file mode 100644
index 0000000000..fe248d00ab
--- /dev/null
+++ b/changelog.d/11830.misc
@@ -0,0 +1 @@
+Correct a type annotation in the event validation logic.
\ No newline at end of file