BUG #18590: during pg14 to pg15 migration , old passwords not migrated to scram-sha from md5

The following bug has been logged on the website:

Bug reference:      18590
Logged by:          kaaa
Email address:      mynagam@gmail.com
PostgreSQL version: 15.0
Operating system:   Linux
Description:

In few upgrades , we see one issue that old user passwords are still with
md5 not with scramsha
In success cases it , says updating passwords and updating schema 
User id: 1 updated its encrypted password successfully.
In the failure cases , it is skipping schema update and and passowrd update
saying User id: 1 already has its encrypted password.