gz-math7 use prerelease for testing

Author: scpeters

plugins/config/repository.yaml

@@ -41,6 +41,12 @@ repositories:
 # wildcards are allowed in name, entries are processed in top-down order
 # first entry matching the name is used
 projects:
+    - name: gz-math7
+      repositories:
+          - name: osrf
+            type: stable
+          - name: osrf
+            type: prerelease
     # Use nightlies in all main branches
     - name: gz-tools3
       repositories: