Group Doctrine workflow updates together

We do very small releases, often touching only one workflow, which means
it is unlikely to have several issues when attempting to bump several
references to this repository.

Author: greg0ire

.github/dependabot.yml

@@ -6,3 +6,7 @@ updates:
       interval: "weekly"
     labels:
       - "CI"
+    groups:
+      doctrine:
+        patterns:
+          - "doctrine/*"