Clear scope transaction name when span is cleared

Restoring scope.span to None after a transaction ends left a stale
_transaction value on the scope, so later errors could inherit the old
transaction name. Clear it when span is set to None.

Fixes #7774

Author: Hashim1999164

sentry_sdk/scope.py

@@ -904,6 +904,10 @@ def span(self) -> "Optional[Span]":
     @span.setter
     def span(self, span: "Optional[Span]") -> None:
         self._span = span
+        if span is None:
+            self._transaction = None
+            self._transaction_info = {}
+            return
         # XXX: this differs from the implementation in JS, there Scope.setSpan
         # does not set Scope._transactionName.
         if isinstance(span, Transaction):

tests/tracing/test_misc.py

@@ -428,6 +428,9 @@ def test_start_transaction_updates_scope_name_source(sentry_init):
         assert scope._transaction == "foobar"
         assert scope._transaction_info == {"source": "route"}
 
+    assert scope._transaction is None
+    assert scope._transaction_info == {}
+
 
 @pytest.mark.parametrize("sampled", (True, None))
 def test_transaction_dropped_debug_not_started(sentry_init, sampled):