Fix.

Author: tobiasraabe

.github/workflows/main.yml

@@ -5,6 +5,9 @@ concurrency:
   group: ${{ github.head_ref || github.run_id }}
   cancel-in-progress: true
 
+env:
+  CONDA_EXE: mamba
+
 on:
   push:
     branches:
@@ -32,12 +35,14 @@ jobs:
         if: runner.os != 'Windows'
       - uses: conda-incubator/setup-miniconda@v2
         with:
-          auto-update-conda: true
+          auto-update-conda: false
           python-version: ${{ matrix.python-version }}
+          channels: conda-forge,nodefaults
+          mamba-version: "*"
 
       - name: Install core dependencies.
         shell: bash -l {0}
-        run: conda install -c conda-forge tox-conda coverage
+        run: mamba install -c conda-forge tox-conda coverage mamba
 
       # Unit, integration, and end-to-end tests.
 
@@ -46,7 +51,7 @@ jobs:
         run: tox -e pytest -- -m "unit or (not integration and not end_to_end)" --cov=./ --cov-report=xml -n auto
 
       - name: Upload coverage report for unit tests and doctests.
-        if: runner.os == 'Linux' && matrix.python-version == '3.9'
+        if: runner.os == 'Linux' && matrix.python-version == '3.8'
         shell: bash -l {0}
         run: bash <(curl -s https://codecov.io/bash) -F unit -c
 
@@ -55,6 +60,6 @@ jobs:
         run: tox -e pytest -- -m end_to_end --cov=./ --cov-report=xml -n auto
 
       - name: Upload coverage reports of end-to-end tests.
-        if: runner.os == 'Linux' && matrix.python-version == '3.9'
+        if: runner.os == 'Linux' && matrix.python-version == '3.8'
         shell: bash -l {0}
         run: bash <(curl -s https://codecov.io/bash) -F end_to_end -c