Docs: Update to mention centos stream 8 instead of centos linux 8

update docs to mention centos stream 8 instead of centos linux 8

Centos Linux 8 is now officially EOL. Let's switch the docs to mention Centos Stream 8 that has support until May 2024.

I tested the workflow and everything seems to work fine. The installation script detects CentOS Stream 8 as centos and correctly uses el/8 repository for it.

As for any concerns with compatibility, the rpm contains just a statically compiled there shouldn't be any issues with CentOS Stream. If some issues appear, it's definitely a bug of CentOS because it should represent the next version of RHEL which is also supported by the el/8 version of the runner rpm package.