Don't abort additional INSERTs when hitting first conflict

When an INSERT with ON CONFLICT DO NOTHING hits the first conflicts
it would abort additional INSERTS following the INSERT triggering
the DO NOTHING clause leading to missed INSERTs.

Fixes #7672

src/nodes/hypertable_modify.c

@@ -728,7 +728,7 @@ ExecModifyTable(CustomScanState *cs_node, PlanState *pstate)
 			cds->skip_current_tuple = false;
 			if (node->ps.instrument)
 				node->ps.instrument->ntuples2++;
-			return NULL;
+			continue;
 		}
 
 		/* No more tuples to process? */