remove bash dependency

[miki725]

Description

Not all GitHub runners have bash installed. For example it might be a self-hosted runner without bash or workflow might be using a container.

Currently cosign action fails with:

Run sigstore/cosign-installer@main
  with:
    cosign-release: v2.4.3
    install-dir: $HOME/.cosign
    use-sudo: false
Run #!/bin/bash
OCI runtime exec failed: exec failed: unable to start container process: exec: "bash": executable file not found in $PATH: unknown

Version

cosign is never installed