no need to specify wagtail>=5.1rc1 now that 5.1 is out

.github/workflows/test.yml

@@ -9,6 +9,7 @@ on:
 # - django 3.2, python 3.8, wagtail 4.1, sqlite
 # - django 4.1, python 3.9, wagtail 4.2, postgresql
 # - django 4.2, python 3.10, wagtail 5.0, sqlite
+# - django 4.2, python 3.11, wagtail 5.1, postgresql
 # - django 4.1, python 3.11, wagtail main, postgres (allow failures)
 jobs:
   test:
@@ -35,7 +36,7 @@ jobs:
             experimental: false
           - python: "3.11"
             django: "Django>=4.2,<4.3"
-            wagtail: "wagtail>=5.1rc1,<5.2"
+            wagtail: "wagtail>=5.1,<5.2"
             database: "postgresql"
             psycopg: "psycopg2>=2.6"
             experimental: false