Bump mamba-org/setup-micromamba from 2 to 3 (#26)

Author: dependabot[bot]

.github/workflows/CI.yaml

@@ -39,7 +39,7 @@ jobs:
           df -h
           ulimit -a
 
-      - uses: mamba-org/setup-micromamba@v2
+      - uses: mamba-org/setup-micromamba@v3
         with:
           environment-file: devtools/conda-envs/test_env.yaml
           environment-name: test