FileAttachment import and call cannot be within the same cell

[cinxmo]

```js echo
import {FileAttachment} from "npm:@observablehq/stdlib";
const v = await FileAttachment("volcano.json").json();
```

displays Error: File not found: volcano.json. The output of parser does not include volcano.json in the list of files

vs this works:

```js echo
import {FileAttachment} from "npm:@observablehq/stdlib";
```

```js echo
const v = await FileAttachment("volcano.json").json();
```