update ncdu to 2.1.2

Summary:

• Still requires Zig 0.9.0 or 0.9.1
• Fix possible crash on shortening file names with unicode variation selectors or combining marks

Test Plan: build,install&run

Reviewers: Triage Team, algent

Reviewed By: Triage Team, algent

Subscribers: algent

Differential Revision: https://dev.getsol.us/D13181