Failure to remove a field results in no other secret fields getting removed

[Code causing issue](https://github.com/canonical/data-platform-libs/blob/045506f777d39d86ed30d540097586ed28003f50/lib/charms/data_platform_libs/v0/data_interfaces.py#L1128-L1137)

## Steps to reproduce
```
self.database_provides.delete_relation_data(
relation.id, fields=["username", "password", "uris", "field-that-cannot-be-removed"]
)
```

## Expected behavior
```
juju show-unit app-name/0
```
shows no secrets for `"username", "password", "uris", `

## Actual behavior
```
juju show-unit app-name/0
```
still has secrets for `"username", "password", "uris", `

## Versions
Juju `3.1.6`, latest lib