E.g. lastcall can exist more than once according to the schema, but only
one item was kept.
Before:
```yaml
lastcall: 2017-11-15
```
After:
```yaml
lastcall:
- 2021-03-30
- 2017-11-15
```
Don't remember why it did this here. There's another spot where it
removes longer stretches of whitespace. Doesn't trim leading or trailing
whitespace tho, but that's what breaks it here.
