1.32: csv rules: adding a newline to comments disables field interpolation

From a report by pepe_pecas in chat:

```csv
2023-01-01,1
```

```csv.rules
fields date, amount
account1 (a)
comment %date \n next line
```

Good:
```cli
$ hledger-1.31 -f a.csv print
2023-01-01  ; 2023-01-01
    ;  next line
    (a)               1
```

Bad:
```cli
$ hledger-1.32 -f a.csv print
2023-01-01  ; %date
    ;  next line
    (a)               1

```

