[yugabyte#24420] YSQL: Fix the NoWaitForRPCOnTermination unit test

Summary:
The `NoWaitForRPCOnTermination` unit test expects that connection will be closed while query processing. The test checks that raised error will have particular message `terminating connection due to administrator command`. This error message with this substring is really logged by postgres in logs, but the postgres process may not sent it to the user. It may just close the connection. As a result client may only detect general connection close error.

Solution: rework the check that connection was closed.
Jira: DB-13330

Test Plan:
Run existing unit test
```
./yb_build.sh --gtest_filter PgMiniTest.NoWaitForRPCOnTermination
```

Reviewers: pjain, jason, kramanathan

Reviewed By: kramanathan

Subscribers: yql

Tags: #jenkins-ready

Differential Revision: https://phorge.dev.yugabyte.com/D39005

Author: d-uspenskiy

src/yb/yql/pgwrapper/pg_mini-test.cc

@@ -2175,11 +2175,7 @@ TEST_F(PgMiniTest, CompactionAfterDBDrop) {
 // The test checks that YSQL doesn't wait for sent RPC response in case of process termination.
 TEST_F(PgMiniTest, NoWaitForRPCOnTermination) {
   auto conn = ASSERT_RESULT(Connect());
-  ASSERT_OK(conn.Execute("CREATE TABLE t(k INT PRIMARY KEY) SPLIT INTO 1 TABLETS"));
-  constexpr auto kRows = RegularBuildVsDebugVsSanitizers(1000000, 100000, 30000);
-  ASSERT_OK(conn.ExecuteFormat(
-      "INSERT INTO t SELECT s FROM generate_series(1, $0) AS s", kRows));
-  constexpr auto kLongTimeQuery = "SELECT COUNT(*) FROM t";
+  constexpr auto kLongTimeQuery = "SELECT pg_sleep(30)";
   std::atomic<MonoTime> termination_start;
   MonoTime termination_end;
   {
@@ -2192,11 +2188,12 @@ TEST_F(PgMiniTest, NoWaitForRPCOnTermination) {
       const auto deadline = MonoTime::Now() + MonoDelta::FromSeconds(30);
       while (MonoTime::Now() < deadline) {
         const auto local_termination_start = MonoTime::Now();
-        auto res = ASSERT_RESULT(thread_conn.FetchFormat(
-          "SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE query like '$0'",
-          kLongTimeQuery));
-        auto lines = PQntuples(res.get());
-        if (lines) {
+        const auto lines = ASSERT_RESULT(thread_conn.FetchRows<bool>(
+            Format(
+                "SELECT pg_terminate_backend(pid) FROM pg_stat_activity WHERE query like '$0'",
+                kLongTimeQuery)));
+        if (!lines.empty()) {
+          ASSERT_TRUE(lines.size() == 1 && lines.front());
           termination_start.store(local_termination_start, std::memory_order_release);
           break;
         }
@@ -2206,8 +2203,8 @@ TEST_F(PgMiniTest, NoWaitForRPCOnTermination) {
     latch.Wait();
     const auto res = conn.Fetch(kLongTimeQuery);
     ASSERT_NOK(res);
-    ASSERT_STR_CONTAINS(res.status().ToString(),
-                        "terminating connection due to administrator command");
+    ASSERT_TRUE(res.status().IsNetworkError());
+    ASSERT_STR_CONTAINS(res.status().ToString(), "server closed the connection unexpectedly");
     termination_end = MonoTime::Now();
   }
   const auto termination_duration =