Bump conda-incubator/setup-miniconda from 2 to 3 (#998)

Bumps [conda-incubator/setup-miniconda](https://github.com/conda-incubator/setup-miniconda) from 2 to 3.
- [Release notes](https://github.com/conda-incubator/setup-miniconda/releases)
- [Changelog](https://github.com/conda-incubator/setup-miniconda/blob/main/CHANGELOG.md)
- [Commits](conda-incubator/setup-miniconda@v2...v3)

---
updated-dependencies:
- dependency-name: conda-incubator/setup-miniconda
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/downstream.yml

@@ -73,7 +73,7 @@ jobs:
         uses: jupyterlab/maintainer-tools/.github/actions/base-setup@v1
 
       - name: Setup conda ${{ matrix.python-version }}
-        uses: conda-incubator/setup-miniconda@v2
+        uses: conda-incubator/setup-miniconda@v3
         with:
           auto-update-conda: true
           activate-environment: jupyter_kernel_test