MINOR: Add ffacs to collaborators list

[ffacs]

Why are the changes needed?

Recently I am active on maintaining C++ codes. The contributions can be seembelow: https://github.com/apache/orc/pulls?q=is%3Apr+author%3Affacs+is%3Aclosed

I want to add myself as collaborators.

How was this patch tested?

No tests

Was this patch authored or co-authored using generative AI tooling?

No

[dongjoon-hyun]

To @wgtmac ,

• If you think @ffacs is a good candidate for Apache ORC C++ part committer, you can nominate him in private mailing list instead.
• Feel free to open a discussion on private list. 😄

[dongjoon-hyun]

Let me close this first.