BUG #16418: postgis23_96 dependency proj49 missing now pgdg94 default to disabled

The following bug has been logged on the website:

Bug reference: 16418
Logged by: Leo Lapworth
Email address: leo.lapworth@kaarbontech.co.uk
PostgreSQL version: 9.6.16
Operating system: Centos 7
Description:

Following on from #16397 (which seems fixed)

I see that [pgdg94] now defaults to disabled...

However postgis23_96 ( from pgdg96/7/x86_64 ) relies on - proj49 - which is
not in pgdg96/7/x86_64

E.g. I can see it here:

https://download.postgresql.org/pub/repos/yum/9.4/redhat/rhel-7.8-x86_64/

But not here:

https://download.postgresql.org/pub/repos/yum/9.6/redhat/rhel-7.8-x86_64/