pgwire: keep query-terminated wording for dropped dependency in FETCH

The FETCH path rendered `PeekResponseUnary::DependencyDropped` via
`to_concurrent_dependency_drop()`, changing the message from "query could
not complete because relation ... was dropped" to "relation '...' was
dropped". Restore `query_terminated_error()` so the message and SQLSTATE
are unchanged; this rendering is out of scope for the evaluation-error
SQLSTATE work and broke `test_subscribe_on_dropped_source`.

Author: antiguru

src/pgwire/src/protocol.rs

@@ -2414,9 +2414,10 @@ where
                             FetchResult::Error(err.into_response(Severity::Error))
                         }
                         Some(PeekResponseUnary::DependencyDropped(dep)) => {
-                            FetchResult::Error(
-                                dep.to_concurrent_dependency_drop().into_response(Severity::Error),
-                            )
+                            FetchResult::Error(ErrorResponse::error(
+                                SqlState::INTERNAL_ERROR,
+                                dep.query_terminated_error(),
+                            ))
                         }
                         Some(PeekResponseUnary::Canceled) => FetchResult::Canceled,
                     },