Run tests only on python 3.7 & 3.9 (#5433)

* Run tests on only python 3.7 & 3.9

Author: max-sixty

.github/workflows/ci.yaml

@@ -37,7 +37,8 @@ jobs:
       fail-fast: false
       matrix:
         os: ["ubuntu-latest", "macos-latest", "windows-latest"]
-        python-version: ["3.7", "3.8", "3.9"]
+        # Bookend python versions
+        python-version: ["3.7", "3.9"]
     steps:
       - uses: actions/checkout@v2
         with:

doc/whats-new.rst

@@ -58,6 +58,9 @@ Documentation
 
 Internal Changes
 ~~~~~~~~~~~~~~~~
+- Run CI on the first & last python versions supported only; currently 3.7 & 3.9.
+  (:pull:`5433`)
+  By `Maximilian Roos <https://github.com/max-sixty>`_.
 
 .. _whats-new.0.18.2: