`libmamba` fails when using `tox-conda`, because `python =3.0x`

[zacharyburnett]

when using conda: true with conda_deps and conda_channel set in the tox.ini, I get the following error:
https://github.com/spacetelescope/wfc3tools/actions/runs/15071133917/job/42367498006#step:6:53

  error    libmamba Could not solve for environment specs
      The following package could not be installed
      └─ python =3.0x * does not exist (perhaps a typo or a missing channel).
  critical libmamba Could not solve for environment specs

here is the YAML:

  test:
    uses: OpenAstronomy/github-actions-workflows/.github/workflows/tox.yml@v1
    with:
      conda: true
      envs: |
        - linux: py311-xdist
        - linux: py312-xdist
        - macos: py312-xdist
        - linux: py3-cov-xdist
          coverage: codecov

From #123, setup-micromamba is using ${{ matrix.python_version }}:

github-actions-workflows/.github/workflows/tox.yml

Line 199 in 4f79fc8

python=${{ matrix.python_version }}

However, I can't find where python_version is being set as 3.0x:

github-actions-workflows/tools/tox_matrix.py

Lines 128 to 137 in 4f79fc8

	# set python_version
	python_version = env.get("python-version")
	m = re.search("^py(2|3)([0-9]+)", item["toxenv"])
	if python_version is not None:
	item["python_version"] = python_version
	elif m is not None:
	major, minor = m.groups()
	item["python_version"] = f"{major}.{minor}"
	else:
	item["python_version"] = env.get("default_python") or default_python

[zacharyburnett]

Oh! It works when I remove all extra toxenv flags:

  test:
    uses: OpenAstronomy/github-actions-workflows/.github/workflows/tox.yml@v1
    with:
      conda: true
      envs: |
        - linux: py311
        - linux: py312
        - macos: py312

There must be something wrong with the regex parsing

[ConorMacBride]

Hi @zacharyburnett, looks like tox_matrix.py is not recognizing py3 in the env name as the regex is also expecting a minor version number. This means the default version is passed in when setting up the conda environment, which we have as 3.x in the tox reusable workflow. 3.x works for the setup python action but not the conda setup. To fix you can specify default_python in the workflow for your py3- tox environment. We should probably fix the incompatible default for conda though.