Golang x/crypto/x509roots: regeneration fails with "404 Not Found"

Attempting to regenerate this package currently fails with:

$ go generate golang.org/x/crypto/x509roots
2025/08/11 15:34:05 got non-200 OK status code: 404 Not Found body: "\nerror: security/nss/lib/ckfw/builtins/certdata.txt@3654da6b808b2eb5628337291235935c662bf711: not found in manifest\n"
exit status 1
gen_fallback_bundle.go:7: running "go": exit status 1

Detected because the relui workflow ran into this.

CC @golang/security.