[CI] Patch `cpp-check` for 2.15 version AND enable DMC repo

Issue 1

Looks like the container image we use for cpp-check has updated the version to 2.15 and this new version requires some changes to the config file we are using. The error:

<error id="normalCheckLevelMaxBranches" severity="information" msg="Limiting analysis of branches. Use --check-level=exhaustive to analyze all branches." verbose="Limiting analysis of branches. Use --check-level=exhaustive to analyze all branches." file0="catalogue/CatalogueSchema.cpp">

Issue 2

Looks like gfal2-util is no longer available from the epel repo. For the time being I have added the dmc repo so that it can be downloaded and the gfal system tests do not fail.