Put ERA5 data on same grid as CDS models

[nhsavage]

to avoid double interpolation ensure we have the same grid for ERA5 as GCMs. This might have changed due to: this https://forum.ecmwf.int/t/software-upgrade-for-data-extraction-of-a-geographical-area-from-selected-era5-and-seasonal-forecast-datasets/14583

Currently:
GCM:
lat:

<xarray.DataArray 'lat' (lat: 25)> Size: 200B
array([54.5, 53.5, 52.5, 51.5, 50.5, 49.5, 48.5, 47.5, 46.5, 45.5, 44.5, 43.5,
       42.5, 41.5, 40.5, 39.5, 38.5, 37.5, 36.5, 35.5, 34.5, 33.5, 32.5, 31.5,
       30.5])

lon:

<xarray.DataArray 'lon' (lon: 30)> Size: 240B
array([-89.5, -88.5, -87.5, -86.5, -85.5, -84.5, -83.5, -82.5, -81.5, -80.5,
       -79.5, -78.5, -77.5, -76.5, -75.5, -74.5, -73.5, -72.5, -71.5, -70.5,
       -69.5, -68.5, -67.5, -66.5, -65.5, -64.5, -63.5, -62.5, -61.5, -60.5])

ERA5:

lat

<xarray.DataArray 'lat' (lat: 26)> Size: 208B
array([55., 54., 53., 52., 51., 50., 49., 48., 47., 46., 45., 44., 43., 42.,
       41., 40., 39., 38., 37., 36., 35., 34., 33., 32., 31., 30.])

lon:

<xarray.DataArray 'lon' (lon: 31)> Size: 248B
array([-90., -89., -88., -87., -86., -85., -84., -83., -82., -81., -80., -79.,
       -78., -77., -76., -75., -74., -73., -72., -71., -70., -69., -68., -67.,
       -66., -65., -64., -63., -62., -61., -60.])