Add solver to test-environment

[skip ci]

.github/workflows/build.yaml

@@ -56,7 +56,6 @@ jobs:
           conda install -c pyviz "pyctdev>=0.5"
           doit ecosystem_setup
           conda install -c conda-forge "urllib3<2.0.0" "conda-build==3.24"
-          conda install -n test-environment conda-libmamba-solver
       - name: conda build
         run: |
           doit package_build --recipe=core $CHANS_DEV $PKG_TEST_PYTHON --test-group=simple
@@ -83,6 +82,7 @@ jobs:
         run: |
           eval "$(conda shell.bash hook)"
           conda activate test-environment
+          conda install conda-libmamba-solver --solver=classic
           doit develop_install $CHANS_DEV -o build
           python setup.py develop
       - name: npm dev deploy