If someone doesn't have code-generator in their GOPATH, they'll need to
run `go mod vendor` to populate the vendor directory with the code-generator
repo (it is required by `hack/tools.go`).
However, `go mod vendor` does not mark scripts as executable which leads to a
`Permission denied` error while trying to run `update-codegen.sh` in staging repos.
So fix scripts to not rely on codegen scripts being executable.
Kubernetes-commit: 391da79abd7a7af1cfab04de35daba7cd58c4c80
