Upgrade cosign version to latest version in GitHub workflows

[rcmadhankumar]

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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