Install required packages for testing

Author: seisman

.github/workflows/ci_tests.yaml

@@ -76,7 +76,11 @@ jobs:
       # Install GMT and other required dependencies from conda-forge
       - name: Install dependencies
         shell: bash -l {0}
-        run: conda env update --file environment.yml
+        run: |
+          conda install gmt=6.1.1 numpy pandas xarray netCDF4 packaging \
+                        codecov coverage[toml] \
+                        pytest-cov pytest-mpl pytest>=6.0 \
+                        ipython
 
       # Show installed pkg information for postmortem diagnostic
       - name: List installed packages