setup-miniconda: Speed up conda install

Specify the channels only where needed (they don't need to be searched
for conda-libmamba-solver).

.github/actions/setup-integration-tests/action.yaml

@@ -25,7 +25,6 @@ runs:
     - uses: conda-incubator/setup-miniconda@v2
       with:
         python-version: ${{ inputs.python-version }}
-        channels: conda-forge,bioconda
         activate-environment: test
 
     - run: |
@@ -43,7 +42,7 @@ runs:
 
     # Install software for the "ambient" runner; not supported on Windows.
     - if: runner.os != 'Windows'
-      run: conda install augur auspice snakemake
+      run: conda install -c bioconda -c conda-forge augur auspice snakemake
       shell: bash -l -eo pipefail {0}
 
     - run: conda info