This PR fixes #6343 by causing the t3c integration tests's Traffic Server RPM SPEC to exclude release candidate tags in the version number.
Before:

trafficserver-8.1.4_rc0-0.965df952e.el8.x86_64.rpm

After:

trafficserver-8.1.3-10-965df952e.el8.x86_64.rpm

This matches the behavior expected by the fetch-github-branch-sha GitHub Action and the ats-version.sh script used by the CDN in a Box makefile, so

• this should make the CDN in a Box GHA workflow pass again
• this should fix ATS RPM caching

Note that the t3c integration tests still fail, but that failure is not caused by this PR.

Which Traffic Control components are affected by this PR?

• Traffic Control Cache Config (t3c, formerly ORT) - ATS RPM
• CDN in a Box - ATS RPM

What is the best way to verify this PR?

Check the RPM name generated by the trafficserver step of the cache-config tests

If this is a bugfix, which Traffic Control versions contained the bug?

• master (a0d33de)

PR submission checklist

• This PR has tests
• This PR has documentation
• This PR has a CHANGELOG.md entry
• This PR DOES NOT FIX A SERIOUS SECURITY VULNERABILITY (see the Apache Software Foundation's security guidelines for details)

Anything else

git describe --exclude='*[^0-9.]*'

would have been cleaner than

git describe --match='*[0-9.][0-9.][0-9.]'

but --exclude is not supported in git version 1.8.3.1, the version used in CentOS 7 currently.