[Core] Silence unnecessary deprecation warnings (#12620)
I noticed during testing that I was getting a lot of these deprecation
warnings about `local_lora_path`:
```
DeprecationWarning: The 'lora_local_path' attribute is deprecated
and will be removed in a future version.
Please use 'lora_path' instead.
```
The check used for emitting this warning was always True, even when the
parameter was not actually specified. It will always be in
`__struct_fields__`. We should be checking for a non-None value,
instead.
Signed-off-by: Russell Bryant <rbryant@redhat.com>
Signed-off-by: Russell Bryant <rbryant@redhat.com>
