ci(dependabot): limit allowed dependency-type

Add allow section with "direct" dependency-type
setting to limit the level of dependencies
considered for updates to only the ones listed
in the project's pyproject.toml file.

.github/dependabot.yml

@@ -20,6 +20,10 @@ updates:
     commit-message:
       prefix: "build"
       include: "scope"
+    allow:
+      # limit updates to direct dependencies, so dependencies of direct
+      # dependencies (like APIS Core) aren't included
+      - dependency-type: "direct"
     groups:
       apis-dependencies:
         patterns: