Upgrade cosign version to latest version in GitHub workflows

**What steps did you take:**
[A clear and concise description steps and any files that can be used to reproduce the problem.]
Cosign version used in GitHub version is v0.5.0 which is very old and the latest version is v2.2.4.
Cosign needs to be updated to the latest version.

**What happened:**
[A small description of the result]

**What did you expect:**
[A description of what was expected]

**Anything else you would like to add:**
[Additional information that will assist in solving the issue.]

**Environment:**

- imgpkg version (use `imgpkg --version`):
- Docker registry used (e.g. `Docker HUB`):
- OS (e.g. from `/etc/os-release`):

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