Adapted custom co2s table to match CMIP6 version

[schlunma]

This PR fixes the custom co2s table to match its CMIP6 version as discussed in #587.

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[mattiarighi]

The tests are failing, but it looks like an internal circleci error.

[schlunma]

I think so too, can we restart the test somehow?

[mattiarighi]

There is a restart button, but I have no rights to trigger a restart.

[schlunma]

Tests are fine now