fix: Update to MorphoCloud/MorphoCloudWorkflow@7817dc8

List of MorphoCloudWorkflow changes:

```
$ git shortlog c9c07b3..7817dc8 --no-merges
Jean-Christophe Fillion-Robin (1):
      fix(create-instance): Attempt to fix networking removing redundant security group
```

See MorphoCloud/MorphoCloudWorkflow@c9c07b3...7817dc8

.github/workflows/create-instance.yml

@@ -219,7 +219,6 @@ jobs:
 
           openstack server create "$INSTANCE_NAME" \
             --nic net-id="auto_allocated_network" \
-            --security-group "default" \
             --security-group "exosphere" \
             --flavor $INSTANCE_FLAVOR \
             --image "Featured-Ubuntu22" \