remove version of mamba from GHA

[paskino]

Description

GHA fails on the conda task because the conda-incubator/setup-miniconda tries to install mamba version 1.15.

CIL/.github/workflows/build.yml

Lines 122 to 126 in 98860db

	- uses: conda-incubator/setup-miniconda@v3
	with:
	python-version: ${{ matrix.python-version }}
	mamba-version: "1.5"
	channels: conda-forge

The error we incur is the following.

/usr/share/miniconda/condabin/conda install --name base mamba=1.5
  CI detected...
  Channels:
   - conda-forge
   - defaults
  Platform: linux-64
  Collecting package metadata (repodata.json): ...working... done
  Solving environment: ...working... failed
  Warning: 
  LibMambaUnsatisfiableError: Encountered problems while solving:
    - nothing provides _python_rc needed by python-3.13.0rc2-h6355ac2_0_cp313t

Probably that's a too old version of mamba which is incompatible with the new conda with python 3.13.

I suggest to remove the pinned version 1.5 of mamba and opt for *, see https://github.com/conda-incubator/setup-miniconda#example-6-mamba

Linked Issues

• closes Github actions failing conda-matrix tests on master #2072
• supersedes Remove defaults channel from requirements-test.yml #2047
• removes a warning, which is removed using the conda-forge channel only:

/usr/share/miniconda/condabin/mamba create --name test python=3.10
  Warning: warning  libmamba 'repo.anaconda.com', a commercial channel hosted by Anaconda.com, is used

Checklist

• I have performed a self-review of my code
• I have added docstrings in line with the guidance in the developer guide
• I have updated the relevant documentation
• I have implemented unit tests that cover any new or modified functionality
• CHANGELOG.md has been updated with any functionality change
• Request review from all relevant developers
• Change pull request label to 'Waiting for review'

Contribution Notes

Please read and adhere to the developer guide and local patterns and conventions.

• The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in CIL (the Work) under the terms and conditions of the Apache-2.0 License
• I confirm that the contribution does not violate any intellectual property rights of third parties

[MargaretDuff]

All tests pass:

[MargaretDuff]

All tests pass on the full matrix, happy to approve

[MargaretDuff]

Closes #2072

[paskino]

Let's merge #2047 to remove all warnings.

[lauramurgatroyd]

I don't think #2047 will remove all of the warnings - when I originally looked at them I thought this would but actually the issue is different: #2051

But anyway the defaults channel is not needed and should be removed from the env file