Checking the contents of the CHANGES file currently requires invokingmultiple shell scripts. These invocations are conflated with those forother test scripts in the "misc" GitLab CI job. Extract the commandschecking the contents of the CHANGES file to a separate GitLab CI job,"changes", to improve readability. Remove similar checks for theCHANGES.SE file altogether as they are only relevant for BIND -S andtherefore should not be present in an open source branch.
Since pre-release testing is usually carried out for branches in whichCHANGES entries are intentionally malformed to prevent entry numberingconflicts down the road, do not run the "changes" GitLab CI job inpipelines that are triggered by a parent pipeline (which can currentlyonly be a pre-release testing pipeline) to prevent triggering jobfailures that would be meaningless anyway.
