[Unit Tests] Reenable `top_scope_context_obj` (#6892)

[Unit Tests] Reenable `top_scope_context_obj` (#6892)

Fixes #6047. The test was disabled because ASan found a use-after-free
due to an object allocated in the top scope being destroyed after the
scope (see #2607 for a detailed explanation). At first, the plan was to
add support for this use case. However, we have decided that we
currently don't need support for this feature and added a guard against
it (#6082). This commit reenables the test but changes it to destroy the
object allocated in the top level scope before the corresponding level
is popped. It additionally adds a test of the guard from #6082.