Update aws.md with updated conda install command

[rzelle-lallemand]

As discussed in e.g. actions/runner-images#12641, recent versions of miniconda are prompting the user to accept the terms of service of the default anaconda channels. This makes the original command $HOME/miniconda/bin/conda install -c conda-forge -y awscli fail:

$ $HOME/miniconda/bin/conda install -c conda-forge -y awscli

CondaToSNonInteractiveError: Terms of Service have not been accepted for the following channels. Please accept                                            or remove them before proceeding:
    - https://repo.anaconda.com/pkgs/main
    - https://repo.anaconda.com/pkgs/r

To accept these channels' Terms of Service, run the following commands:
    conda tos accept --override-channels --channel https://repo.anaconda.com/pkgs/main
    conda tos accept --override-channels --channel https://repo.anaconda.com/pkgs/r

For information on safely removing channels from your conda configuration,
please see the official documentation:

    https://www.anaconda.com/docs/tools/working-with-conda/channels

This PR circumvents the Terms of Service acceptance prompt for miniconda's default "main" and "r" channels, by overriding the lookup channels to just "conda-forge" through the use of the "--override-channels" flag.

Alternative, the instructions could switch from using miniconda to something like miniforge which defaults to only using conda-forge.

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