Add test runs against ubuntu-18.04 and macos-11.0.

Author: kdeldycke

.github/workflows/tests.yaml

@@ -13,8 +13,16 @@ jobs:
     runs-on: ${{matrix.os}}
     strategy:
       matrix:
-        os: [ubuntu-latest, macos-latest, windows-latest]
-        python-version: [3.7, 3.8, 3.9]
+        os:
+          - ubuntu-20.04
+          - ubuntu-18.04
+          - macos-11.0
+          - macos-10.15
+          - windows-2019
+        python-version:
+          - "3.9"
+          - "3.8"
+          - "3.7"
     steps:
       - uses: actions/[email protected]
       - name: Set up Python ${{matrix.python-version}}

changelog.rst

@@ -7,6 +7,9 @@ ChangeLog
 
 .. note:: This version is not yet released and is under active development
 
+* Add test runs against new OSes and distributions: ``ubuntu-18.04`` and
+  ``macos-11.0``.
+
 
 `6.0.2 (2020-11-05) <https://github.com/kdeldycke/mail-deduplicate/compare/v6.0.1...v6.0.2>`_
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