Update PgLastStatementSample.java with fixed regions

Author: sgorse123

samples/snippets/src/main/java/com/example/spanner/PgLastStatementSample.java

@@ -42,7 +42,7 @@ static void insertAndUpdateUsingLastStatement() {
         }
     }
 
-    // [START pg_spanner_last_statement]
+    // [START spanner_postgresql_last_statement]
     static void insertAndUpdateUsingLastStatement(DatabaseClient client) {
         client
                 .readWriteTransaction()
@@ -64,6 +64,6 @@ static void insertAndUpdateUsingLastStatement(DatabaseClient client) {
                             return null;
                         });
     }
-    // [END pg_spanner_last_statement]
+    // [END spanner_postgresql_last_statement]
 
 }