databases/imposm3: fix build on arm64, riscv64

Bump golang.org/x/sys dependency to a version new enough
to support aarch64-freebsd and riscv64-freebsd.

Approved by: portmgr (build fix blanket)
MFH: 2024Q4

(cherry picked from commit 1955155ac2df53b15a650e1da2f640b4a1db080b)