Re-install conda/mamba for every tljh upgrade (doesn't imply upgrade)

[consideRatio]

We have previously re-installed (without upgrading) conda and mamba, and done it based on specific versions. I think we are required to do this uncodntionally though. I think based https://github.com/conda/conda/issues/12366#issuecomment-1466144007 that since tljh make use of both pip and conda/mamba to install packages via plugins, even though we mostly use pip, we must do this re-install to ensure conda/mamba is functional before an tljh upgrade.

I think we end up with requests installed via pip during the initial setup of tljh, and that sets us up for issues when we are to make an upgrade later when conda/mamba is being used via plugins. I think the reason we didn't have this error before in tests, but do now, relates to new versions of openssl have been released, and that conda/mamba automatically upgrades them.

• Fixes #944

[consideRatio]

@manics @minrk this may be relevant to ensure upgrade works, especially soon if users are to use the upgrade to get security patches or similar.