Modernize GitHub Actions test runner

Author: Repiteo

.appveyor.yml

@@ -5,10 +5,9 @@
 # This is slow, try to keep the number of builds as low as makes sense.
 
 image:
-  # linux builds done in Travis CI for now
+  # Test images unsupported by GitHub Actions.
   - Visual Studio 2017
   - Visual Studio 2019
-  - Visual Studio 2022
 
 cache:
   - downloads -> appveyor.yml
@@ -34,38 +33,9 @@ environment:
   COVERAGE: 0
   SCONS_CACHE_MSVC_CONFIG: "true"
   matrix:
-    # Test oldest and newest supported Pythons, and a subset in between.
-    # Skipping 3.8, 3.10, 3.12 at this time
-    - WINPYTHON: "Python313"
-    - WINPYTHON: "Python311"
+    # Test oldest and newest supported Pythons.
+    - WINPYTHON: "Python314"
     - WINPYTHON: "Python39"
-    - WINPYTHON: "Python37"
-
-# remove sets of build jobs based on criteria below
-# to fine tune the number and platforms tested
-matrix:
-  exclude:
-    # test python 3.7 on Visual Studio 2017 image
-    - image: Visual Studio 2017
-      WINPYTHON: "Python313"
-    - image: Visual Studio 2017
-      WINPYTHON: "Python311"
-    - image: Visual Studio 2017
-      WINPYTHON: "Python39"
-
-    # test python 3.9 on Visual Studio 2019 image
-    - image: Visual Studio 2019
-      WINPYTHON: "Python313"
-    - image: Visual Studio 2019
-      WINPYTHON: "Python311"
-    - image: Visual Studio 2019
-      WINPYTHON: "Python37"
-
-    # test python 3.11, 3.13 on Visual Studio 2022 image
-    - image: Visual Studio 2022
-      WINPYTHON: "Python39"
-    - image: Visual Studio 2022
-      WINPYTHON: "Python37"
 
 # Remove some binaries we don't want to be found
 # Note this is no longer needed, git-windows bin/ is quite minimal now.