Only run wal_explain test on PG17+

wal_explain can be flaky at times so skip it on older PG versions

Author: svenklemm

tsl/test/sql/CMakeLists.txt

@@ -110,11 +110,6 @@ set(TEST_TEMPLATES
     transparent_decompression.sql.in
     transparent_decompression_ordered_index.sql.in)
 
-# WAL numbers will differ on 32-bit platform so we only run on 64-bit
-if("${CMAKE_SIZEOF_VOID_P}" STREQUAL "8")
-  list(APPEND TEST_FILES explain_wal.sql)
-endif()
-
 if(USE_TELEMETRY)
   list(APPEND TEST_FILES bgw_telemetry.sql)
 endif()
@@ -227,6 +222,12 @@ if((${PG_VERSION_MAJOR} GREATER_EQUAL "16"))
 endif()
 
 if((${PG_VERSION_MAJOR} GREATER_EQUAL "17"))
+  # WAL numbers will differ on 32-bit platform so we only run on 64-bit only run
+  # on PG17+ since the test can be flaky at times
+  if("${CMAKE_SIZEOF_VOID_P}" STREQUAL "8")
+    list(APPEND TEST_FILES explain_wal.sql)
+  endif()
+
   list(APPEND TEST_FILES privilege_maintain.sql
        merge_append_partially_compressed.sql)
 endif()