Try testing for py2 in a container

.github/workflows/pythonpackage.yml

@@ -34,3 +34,20 @@ jobs:
     - name: Run the tests
       run: |
         cd tests; find . -name 'test_*.py' -print0 | xargs -0 -n1 env PYTHONPATH=.. python
+
+  tests-py2:
+    runs-on: 'ubuntu-20.04'
+      container:
+        image: python:2.7.18-buster
+    steps:
+    - uses: actions/checkout@v3
+    - name: Install dependencies
+      run: |
+        sudo apt-get update
+        sudo apt-get install libhdf5-serial-dev
+        python -m pip install --upgrade pip
+        pip install numpy
+        pip install -r test-requirements.txt
+    - name: Run the tests
+      run: |
+        cd tests; find . -name 'test_*.py' -print0 | xargs -0 -n1 env PYTHONPATH=.. python

CHANGELOG

@@ -2,7 +2,7 @@
 -------
 
  - Make :py:func:`pyteomics.mgf.write` work with a regular list of ints as "charge" param.
- - Fix #115.
+ - Fix #115 and #118.
  - Add mean absolute error (MAE) regression in :py:mod:`pyteomics.achrom`
    (`#117 <https://github.com/levitsky/pyteomics/pull/117>`_ by Mark Ivanov).