Update dependabot config

This change updates the dependabot config to be more restrictive.

We only allow gomod updates to github.com/opencontainers/runtime-spec for gomod
dependencies and all github action updates.

Signed-off-by: Evan Lezar <elezar@nvidia.com>

Author: elezar

.github/dependabot.yml

@@ -5,16 +5,9 @@ updates:
   schedule:
     interval: weekly
   open-pull-requests-limit: 10
-  ignore:
-  - versions: ["*-rc.*"]
-
-- package-ecosystem: gomod
-  directory: "test/tools"
-  schedule:
-    interval: weekly
-  open-pull-requests-limit: 10
-  ignore:
-  - versions: ["*-rc.*"]
+  allow:
+  - dependency-name: "github.com/opencontainers/runtime-spec"
+    dependency-type: direct
 
 - package-ecosystem: "github-actions"
   directory: "/"