Explain commented out CI steps

.github/workflows/python-app.yaml

@@ -1,6 +1,3 @@
-# This workflow will install Python dependencies and run tests
-# For more information see: https://help.github.com/actions/language-and-framework-guides/using-python-with-github-actions
-
 name: Python application
 
 on:
@@ -12,31 +9,44 @@ on:
 jobs:
   build:
 
-    runs-on: ubuntu-latest
+    # we find that CPU/memory limits are less often exceeded using this 
+    # specific version of Ubuntu
+    runs-on: ubuntu-20.04
+
+    #runs-on: ubuntu-latest
+
 
     steps:
     - uses: actions/checkout@v2
     - name: Set up Python 3.9
       uses: actions/setup-python@v2
       with:
         python-version: 3.9
-    - name: pip installation test
+
+    - name: pip installation
+    # test pip installation first (much faster than conda)
       run: |
          pip install --upgrade pip
          pip install -e .
-    - name: Basic checks
+    - name: Basic tests
       run: |
          python tests/check_import.py
          python tests/check_entry_points.py
          bash tests/check_examples.bash
-    - name: Integration tests
+    - name: Advanced tests
       run: |
          bash data/examples/unpack.bash
          bash data/tests/unpack.bash
          python tests/benchmark_cap_vs_mtuq.py --no_figures
          python tests/test_grid_search_mt.py --no_figures
          python tests/test_grid_search_mt_depth.py --no_figures
-#   - name: Conda installation tests
-#     run: |
-#        bash tests/conda_install.bash
+
+    # unfortunately, these Conda installation tests exceed the resource limits
+    # for GitHub workflows
+    # (https://github.com/actions/runner-images/issues/6680)
+    # (https://github.com/conda/conda/issues/8650)
+    #- name: conda installation
+    #  timeout-minutes: 60
+    #  run: |
+    #     bash tests/conda_install.bash
 

env.yaml

@@ -1,5 +1,6 @@
 dependencies:
   - conda-build
+  - python=3
   - numpy 
   - scipy 
   - obspy 

tests/conda_install.bash

@@ -17,7 +17,6 @@ MTUQ_PATH=$(dirname ${BASH_SOURCE[0]})/..
 # mtuq/docs/install/env_conda.rst
 #
 PYTHON_VERSION=3
-DEPENDENCIES="conda-build numpy scipy obspy instaseis pandas xarray netCDF4 h5py mpi4py retry"
 
 
 #
@@ -89,15 +88,15 @@ conda_update $CONDA_PATH >> tests/log1
 echo SUCCESS
 echo
 
-echo "Testing mtuq installation without PyGMT"
-conda env create -q --name env_step2 python=$PYTHON_VERSION --file env.yaml > tests/log2
+echo "Testing mtuq installation"
+conda env create -q --name env_step2 --file env.yaml > tests/log2
 conda activate env_step2
 conda deactivate
 echo SUCCESS
 echo 
 
 echo "Testing mtuq installation with PyGMT"
-conda env create -q --name env_step3 python=$PYTHON_VERSION --file env.yaml > tests/log3
+conda env create -q --name env_step3 --file env.yaml > tests/log3
 conda activate env_step3
 conda install pygmt >> tests/log3
 conda deactivate