Disable cta-ci-others repo before upgrading Oracle

The cta-ci-others internal repository is currently enabled, but is not used for anything, since the Oracle RPMs are installed via the installOracle21.sh script.

However, this is preventing a smooth upgrade of the Oracle client, since adding a new Oracle version to the cta-ci-others repo will cause existing builds to use this new version and break. As such, this should be disabled first, and then in the upgrade, the repo can be enabled again.

See #763 (closed)