CI: Pin micromamba to 1.x (pandas-dev#59912)

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

@@ -9,6 +9,8 @@ runs:
     - name: Install ${{ inputs.environment-file }}
       uses: mamba-org/setup-micromamba@v1
       with:
+        # Pinning to avoid 2.0 failures
+        micromamba-version: '1.5.10-0'
         environment-file: ${{ inputs.environment-file }}
         environment-name: test
         condarc-file: ci/.condarc