BUG #17189: Index not created when primary key created

The following bug has been logged on the website:

Bug reference:      17189
Logged by:          Puneet Sharma
Email address:      puneet.orcl@gmail.com
PostgreSQL version: 12.0
Operating system:   Linux
Description:

I have created the composite primary key which is created successfully but i
am not getting the index against the primary key.

When i created a select query and includes the primary key column it is
going with full table scan. Even i am creating an index on the columns it is
also going with full table scan.