Set strict channel priority to conda-forge only with no

defaults to see if it speeds up resolver. See also
https://docs.conda.io/projects/conda/en/latest/user-guide/tasks/manage-channels.html#strict-channel-priority

Author: weiji14

.github/workflows/ci_tests.yaml

@@ -84,16 +84,17 @@ jobs:
         with:
           activate-environment: pygmt
           python-version: ${{ matrix.python-version }}
-          environment-file: environment.yml
-          miniforge-variant: Mambaforge
+          channels: conda-forge,nodefaults
+          channel-priority: strict
           miniforge-version: latest
+          miniforge-variant: Mambaforge
           mamba-version: "*"
           use-mamba: true
 
       # Install GMT and other required dependencies from conda-forge
       - name: Install dependencies
         run: |
-          conda install gmt=6.2.0 numpy=${{ matrix.numpy-version }} \
+          mamba install gmt=6.2.0 numpy=${{ matrix.numpy-version }} \
                         pandas xarray netCDF4 packaging \
                         ${{ matrix.optional-packages }} \
                         codecov coverage[toml] dvc ipython make \