Add tomli as a dependency in GitHub Actions CI (#1564)

Adding tomli to fix the GitHub Actions CI test
breakages reported in #1392. This is a temporary
measure until `pytest-cov>2.12.1` is released.

* Remove coverage dependency since it is required by pytest-cov already

Author: weiji14

.github/workflows/ci_tests.yaml

@@ -96,8 +96,8 @@ jobs:
           mamba install gmt=6.2.0 numpy=${{ matrix.numpy-version }} \
                         pandas xarray netCDF4 packaging \
                         ${{ matrix.optional-packages }} \
-                        coverage[toml] dvc=2.3.0 make pytest>=6.0 \
-                        pytest-cov pytest-mpl sphinx-gallery
+                        dvc=2.3.0 make pytest>=6.0 \
+                        pytest-cov pytest-mpl sphinx-gallery tomli
 
       # Show installed pkg information for postmortem diagnostic
       - name: List installed packages

environment.yml

@@ -16,7 +16,6 @@ dependencies:
     # Development dependencies
     - black
     - blackdoc
-    - coverage[toml]
     - docformatter
     - dvc=2.3.0
     - flake8