renovatebot(deps): update i2incommon/grouper docker tag to v5.15.4

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [i2incommon/grouper](https://redirect.github.com/rocky-linux/rocky-toolbox-images) | patch | `5.15.3` -> `5.15.4` |

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ci/tests/grouper/docker-compose.yml

@@ -8,7 +8,7 @@ services:
       - POSTGRES_USER=postgres
       - POSTGRES_PASSWORD=pass
   grouper:
-    image: "i2incommon/grouper:5.15.3"
+    image: "i2incommon/grouper:5.15.4"
     restart: always
     container_name: grouper-core
     ports:
@@ -31,7 +31,7 @@ services:
       timeout: 10s
       retries: 5
   grouper-ws:
-    image: "i2incommon/grouper:5.15.3"
+    image: "i2incommon/grouper:5.15.4"
     restart: always
     container_name: grouper-ws
     depends_on: