CI: Fix windows environment setup with micromamba

Apparently broken by micromamba 2.0.3, so fix version back to something
that works. Also go ahead and remove the manual environment name, since
that's completely unused.

.github/actions/install-conda/action.yml

@@ -18,7 +18,7 @@ runs:
     - name: Set up Python ${{ inputs.python-version }}
       uses: mamba-org/setup-micromamba@v2
       with:
-        environment-name: CI
+        micromamba-version: 2.0.2-2
         create-args: python=${{ inputs.python-version }}
         condarc: |
           channels: