fix(serializer): Add type annotations to databag limits (#7505)

### Description
Add `int` annotations to `MAX_DATABAG_DEPTH` and `MAX_DATABAG_BREADTH`
in `serializer.py`.

Without them, ty infers the variables as `Literal[5]` / `Literal[10]`
and reports `invalid-assignment` when users reassign them (e.g.
`sentry_sdk.serializer.MAX_DATABAG_DEPTH = 15`). I checked this with ty
locally: the errors go away after this change. No runtime change.

As discussed in the issue, `MAX_EVENT_BYTES` is left as is.

This is my first open source contribution ever, so thanks @sentrivana
for the quick reply on the issue, and I'm happy to make any changes if
needed!

#### Issues
* resolves: #7503
* resolves: PY-2782

Author: 8rulerstar

sentry_sdk/serializer.py

@@ -43,8 +43,8 @@
 
 # Maximum depth and breadth of databags. Excess data will be trimmed. If
 # max_request_body_size is "always", request bodies won't be trimmed.
-MAX_DATABAG_DEPTH = 5
-MAX_DATABAG_BREADTH = 10
+MAX_DATABAG_DEPTH: int = 5
+MAX_DATABAG_BREADTH: int = 10
 CYCLE_MARKER = "<cyclic>"