Use SHA256 fingerprint instead of MD5 for LFS token secret

What does this MR do and why?

Contributes to #355878 (closed)

Problem

FIPS restricted environments don't support MD5 fingerprints. LFS secrets based on MD5 fingerprint won't work in FIPS mode.

Solution

Use SHA256 fingerprint as a base for secret generation.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.