rename_labels doesn't work with duplicate add_dimension

[soxofaan]

From https://discuss.eodc.eu/t/renaming-existing-bands-bugged/442

It took a while to trim the issue down to the following minimal use case.
The original case had resample_spatial and merge_cubes in it, which seemed like more probable sources of the bug,
but it just turned out that the user accidentally had two time same add_dimension in process graph, and that caused rename_labels to not work anymore.

Anyway, this is minimal use case:

connection = openeo.connect("openeo.vito.be").authenticate_oidc()

bbox = {"west": 4, "south": 51, "east":4.1, "north": 51.1}
dates = ["2022-07-01", "2022-08-01"]
cube = (
    connection.load_collection(
        "SENTINEL2_L2A", spatial_extent=bbox, temporal_extent=dates,
        bands=["B02"]
    )
    .drop_dimension("bands")
    .add_dimension("bands", label="B02", type="bands")
    .add_dimension("bands", label="B02", type="bands")
    .rename_labels("bands", source=["B02"], target=["Blue"])
)
cube.download(outdir / "minimal.nc")
print(list(xarray.load_dataset(outdir / "minimal.nc").data_vars.keys()))
# Results in: ['crs', 'B02']

When removing the duplicate add_dimension, the result is correct:

['crs', 'Blue']