org-persist: Fix expiry check

* lisp/org-persist.el (org-persist--gc-expired-p): Fix incorrect plist
key.

lisp/org-persist.el

@@ -344,8 +344,8 @@ FORMAT and ARGS are passed to `message'."
      (`nil t)
      (`never nil)
      ((pred numberp)
-      (when (plist-get ,collection :access-time)
-        (<= (float-time) (+ (plist-get ,collection :access-time) (* ,cnd 24 60 60)))))
+      (when (plist-get ,collection :last-access)
+        (<= (float-time) (+ (plist-get ,collection :last-access) (* ,cnd 24 60 60)))))
      ((pred functionp)
       (funcall ,cnd ,collection))
      (_ (error "org-persist: Unsupported expiry type %S" ,cnd))))