upgrade to keripy 1.2.8

[dhh1128]

See email from GLEIF, recommending this change.

[dhh1128]

[from twin in jira]
This issue is being tracked in jira at https://eipi.atlassian.net/browse/DF-2643.
To send new comments there, start them with 'Tell jira:'.
The issue is assigned in jira to Cal Warshaw.
As of 2025-06-04T16:19Z, the status of the issue in jira is 'to do'.