.github: Stop testing against Fedora 31

Fedora 31 has now reached its EOL.
diff --git a/.github/compose/ci.docker-compose.yml b/.github/compose/ci.docker-compose.yml
index 8eed4b4..2ef1a24 100644
--- a/.github/compose/ci.docker-compose.yml
+++ b/.github/compose/ci.docker-compose.yml
@@ -22,10 +22,6 @@
 
 services:
 
-  fedora-31:
-    <<: *tests-template
-    image: registry.gitlab.com/buildstream/buildstream-docker-images/testsuite-fedora:31-${CI_IMAGE_VERSION:-latest}
-
   fedora-32:
     <<: *tests-template
 
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 28bb08c..d9401b4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -45,7 +45,6 @@
         # "../compose/ci.docker-compose.yml"
         test-name:
           - debian-10
-          - fedora-31
           - fedora-32
           - fedora-33
           - ubuntu-18.04