Fix recipe_correlation.yml

[bouweandela]

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Closes #1477

[mattiarighi]

Still not running

Traceback (most recent call last):
  File "/mnt/lustre01/pf/b/b309057/ESMValTool/public/esmvaltool/diag_scripts/examples/correlate.py", line 94, in <module>
    main(config)
  File "/mnt/lustre01/pf/b/b309057/ESMValTool/public/esmvaltool/diag_scripts/examples/correlate.py", line 76, in main
    coord = dataset.coord(ref_coord)
  File "/work/bd0080/b309057/SOFTWARE/miniconda3/envs/esmvaltool/lib/python3.8/site-packages/iris/cube.py", line 1497, in coord
    raise iris.exceptions.CoordinateNotFoundError(msg)
iris.exceptions.CoordinateNotFoundError: 'Expected to find exactly 1 air_pressure coordinate, but found none.'

[bouweandela]

This happens because the `positive' = 'down' attribute is missing from the cmorized air_pressure coordinate of the ERA-Interim data. This looks like a bug in the ERA-Interim CMORizer.

[bouweandela]

Created an issue for that here: #1770