[Release] Automated release signing CI uses wrong variable name

[kou]

Describe the bug, including details regarding any error messages, version, and platform.

arrow/.github/workflows/release_candidate.yml

Line 99 in a23c2c7

--local-user "${ARROW_GPG_SECRET_KEY}" \

must use ARROW_GPG_KEY_UID not ARROW_GPG_SECRET_KEY.

Component(s)

Release

[kou]

Issue resolved by pull request 47062
#47062