Add dummy extension with an empty diff

Author: asgerf

ruby/ql/lib/emptydiff.model.yml

@@ -0,0 +1,6 @@
+extensions:
+  - addsTo:
+      pack: codeql/util
+      extensible: restrictAlertsTo
+    data:
+      - ["dummy", 1, 1]

ruby/ql/lib/qlpack.yml

@@ -16,4 +16,5 @@ dependencies:
 dataExtensions:
   - codeql/ruby/frameworks/**/model.yml
   - codeql/ruby/frameworks/**/*.model.yml
+  - '*.model.yml'
 warnOnImplicitThis: true