Allow github actions to test wagtail 4

Author: nickmoreton

.github/workflows/test.yml

@@ -7,6 +7,7 @@ on:
     branches: [master]
 
 # Current configuration:
+# - python 3.10, wagtail 4.0
 # - python 3.9, wagtail 3.0
 # - python 3.8, wagtail 2.16
 # - python 3.7, django 2.15
@@ -18,9 +19,11 @@ jobs:
     strategy:
       matrix:
         include:
+          - python: "3.10"
+            wagtail: wagtail>=4.0,<5.0
+            latest: true
           - python: 3.9
             wagtail: wagtail>=3.0,<4.0
-            latest: true
           - python: 3.8
             wagtail: wagtail>=2.16,<3.0
           - python: 3.7
@@ -42,4 +45,4 @@ jobs:
       - if: ${{ matrix.latest }}
         uses: codecov/codecov-action@v2
         with:
-          name: Python 3.9
+          name: Python 3.9