Fix CI PMS Docker image caching

[JonnyWong16]

Description

Docker manifest v2 doesn't provide the digest hash. It is just calculated as the SHA256 hash of the manifest.

Ref: https://stackoverflow.com/a/78711220

Also always cache the PMS Docker image even if the tests fail.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated the docstring for new or existing methods
• I have added tests when applicable