Only have a single Begin transaction method

bench_test.go

@@ -349,7 +349,7 @@ func benchmarkWriteNRowsViaInsert(b *testing.B, n int) {
 	for i := 0; i < b.N; i++ {
 		src := newBenchmarkWriteTableCopyFromSrc(n)
 
-		tx, err := conn.Begin()
+		tx, err := conn.Begin(context.Background(), nil)
 		if err != nil {
 			b.Fatal(err)
 		}
@@ -388,7 +388,7 @@ func multiInsert(conn *pgx.Conn, tableName string, columnNames []string, rowSrc
 	}
 	resetQuery()
 
-	tx, err := conn.Begin()
+	tx, err := conn.Begin(context.Background(), nil)
 	if err != nil {
 		return 0, err
 	}