That error means that RHEL-8 has that package src.rpm already in its set of shipped packages
[smooge@batcave01 latest]$ rpm -qip ./x86_64/RHEL-8-001/non_modular/python3-scons-3.0.1-8.el8.noarch.rpm
Name : python3-scons
Version : 3.0.1
Release : 8.el8
Architecture: noarch
Install Date: (not installed)
Group : Unspecified
Size : 3816043
License : MIT
Signature : RSA/SHA256, 2018-12-15T01:03:42 UTC, Key ID 199e2f91fd431d51
Source RPM : scons-3.0.1-8.el8.src.rpm
Build Date : 2018-08-12T18:04:25 UTC
Build Host :
s390-015.build.eng.bos.redhat.comRelocations : (not relocatable)
Packager : Red Hat, Inc. <
http://bugzilla.redhat.com/bugzilla>
Vendor : Red Hat, Inc.
URL :
http://www.scons.orgSummary : An Open Source software construction tool
Description :
SCons is an Open Source software construction tool--that is, a build
tool; an improved substitute for the classic Make utility; a better way
to build software. SCons is based on the design which won the Software
Carpentry build tool design competition in August 2000.