As @aiyengar2 has pointed out, it looks like the invalid checksum message is coming from the go-git library here. It seems to occur specifically when retrieving the repo's information to check if the working tree is clean, see here.
Deleting my fork, recreating and re-attempting a make validate (with or without making any actual changes) results in the same error.
Not sure if local versions of these matter but here are my git and go versions
- git version: 2.38.0
- go version: 1.18
on local dev-v2.7:

on upstream dev-v2.7:

make validate result:

current commit hash comparison:

