fix(tracing): Use hasattr for _ctx_token (#4541)

We currently use an `if self._ctx_token` check to determine if a span
has a `_ctx_token`. However, this check is incorrect, since `_ctx_token`
is only sometimes set. Furthermore, when `_ctx_token` is set, we should
always have a `_ctx_token`.

Therefore, using `hasattr` is what we want.

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Author: szokeasaurusrex

sentry_sdk/tracing.py

@@ -248,7 +248,7 @@ def activate(self) -> None:
         self._ctx_token = context.attach(ctx)
 
     def deactivate(self) -> None:
-        if self._ctx_token:
+        if hasattr(self, "_ctx_token"):
             context.detach(self._ctx_token)
             del self._ctx_token