[#24283] YSQL: Fix asan issue in isolation regress test framework

Summary:
Fix asan failure for tests running the isolation regress
framework: org.yb.pgsql.TestPgRegressWaitQueues,
org.yb.pgsql.TestPgRegressIsolationWithoutWaitQueues and
org.yb.pgsql.TestPgRegressIsolation.

The failure is:
```
+=================================================================
+==31476==ERROR: LeakSanitizer: detected memory leaks
+
+Direct leak of 864 byte(s) in 4 object(s) allocated from:
+    #0 0x55fc1116466e in malloc /opt/yb-build/llvm/yb-llvm-v17.0.6-yb-1-1720414757-9b881774-almalinux8-x86_64-build/src/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:69:3
+    #1 0x7f94aa200490 in PQmakeEmptyPGresult /share/jenkins/workspace/github-yugabyte-db-alma8-master-clang17-asan/yugabyte-db/src/postgres/src/interfaces/libpq/../../../../../../src/postgres/src/interfaces/libpq/fe-exec.c:164:24
+    #2 0x7f94aa21df9d in getRowDescriptions /share/jenkins/workspace/github-yugabyte-db-alma8-master-clang17-asan/yugabyte-db/src/postgres/src/interfaces/libpq/../../../../../../src/postgres/src/interfaces/libpq/fe-protocol3.c
+    #3 0x7f94aa21c0bc in pqParseInput3 /share/jenkins/workspace/github-yugabyte-db-alma8-master-clang17-asan/yugabyte-db/src/postgres/src/interfaces/libpq/../../../../../../src/postgres/src/interfaces/libpq/fe-protocol3.c:324:11
+    #4 0x7f94aa207028 in parseInput /share/jenkins/workspace/github-yugabyte-db-alma8-master-clang17-asan/yugabyte-db/src/postgres/src/interfaces/libpq/../../../../../../src/postgres/src/interfaces/libpq/fe-exec.c:2014:2
+    #5 0x7f94aa207028 in PQgetResult /share/jenkins/workspace/github-yugabyte-db-alma8-master-clang17-asan/yugabyte-db/src/postgres/src/interfaces/libpq/../../../../../../src/postgres/src/interfaces/libpq/fe-exec.c:2100:3
+    #6 0x7f94aa208437 in PQexecFinish /share/jenkins/workspace/github-yugabyte-db-alma8-master-clang17-asan/yugabyte-db/src/postgres/src/interfaces/libpq/../../../../../../src/postgres/src/interfaces/libpq/fe-exec.c:2417:19
+    #7 0x7f94aa208437 in PQexecParams /share/jenkins/workspace/github-yugabyte-db-alma8-master-clang17-asan/yugabyte-db/src/postgres/src/interfaces/libpq/../../../../../../src/postgres/src/interfaces/libpq/fe-exec.c:2279:9
+    #8 0x55fc111a2881 in main /share/jenkins/workspace/github-yugabyte-db-alma8-master-clang17-asan/yugabyte-db/src/postgres/src/test/isolation/../../../../../../src/postgres/src/test/isolation/isolationtester.c:201:9
+    #9 0x7f94a8caa7e4 in __libc_start_main (/lib64/libc.so.6+0x3a7e4) (BuildId: 37e4ac6a7fb96950b0e6bf72d73d94f3296c77eb)
+
+Objects leaked above:
+0x511000004640 (216 bytes)
+0x511000008ec0 (216 bytes)
+0x5110000133c0 (216 bytes)
+0x5110000179c0 (216 bytes)
```
Jira: DB-13172

Test Plan: Jenkins: test regex: .*RegressIsolation.*|.*RegressWaitQueues.*

Reviewers: patnaik.balivada

Reviewed By: patnaik.balivada

Subscribers: jason, yql

Differential Revision: https://phorge.dev.yugabyte.com/D40987

src/postgres/src/test/isolation/isolationtester.c

@@ -212,6 +212,8 @@ main(int argc, char **argv)
 			exit(1);
 		}
 
+		PQclear(res); /* YB: Clear res to avoid asan memory leak failure */
+
 		/* Save each connection's backend PID for subsequent use. */
 		conns[i].backend_pid = PQbackendPID(conns[i].conn);
 		conns[i].backend_pid_str = psprintf("%d", conns[i].backend_pid);