fix(actions): default GH_TOKEN input to github.token for backward compat

Author: tannerlinsley

.github/changeset-preview/action.yml

@@ -3,7 +3,8 @@ description: Generates comment on a PR showing expected version impact
 inputs:
   GH_TOKEN:
     description: GitHub token used to post the preview comment
-    required: true
+    required: false
+    default: ${{ github.token }}
 runs:
   using: composite
   steps:

.github/comment-on-release/action.yml

@@ -6,7 +6,8 @@ inputs:
     required: true
   GH_TOKEN:
     description: GitHub token used to comment on PRs and issues
-    required: true
+    required: false
+    default: ${{ github.token }}
 runs:
   using: composite
   steps: