Update docker image for matrix

Author: cscollett

.github/workflows/docker-matrix.yml

@@ -10,7 +10,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        image-tag: ['3.12-slim-bullseye', '3.13-slim-bullseye']
+        image-tag: ['3.13-slim-bullseye', '3.14-rc-slim-bullseye']
         update-strategy: [default, minor]
 
     steps: