ci: accept (and ignore) the branch input from percy/cli SDK regression (#17)

The percy/cli regression fan-out dispatches every SDK's test.yml with
{branch: <cli branch>}. This workflow declared no inputs, so the
dispatch API rejected it with 422 'Unexpected inputs provided'. Declare
the input for dispatch compatibility; the suite itself never installs
@percy/cli, so the value is unused.

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

Author: pranavz28

.github/workflows/test.yml

@@ -10,6 +10,15 @@ on:
   pull_request:
     branches: [main, master]
   workflow_dispatch:
+    inputs:
+      # Sent by percy/cli's SDK regression fan-out. Accepted for dispatch
+      # compatibility but unused: these tests exercise the GraalJS scripts in
+      # a vm harness and never install @percy/cli.
+      branch:
+        description: CLI branch (ignored by this suite)
+        required: false
+        type: string
+        default: master
 
 jobs:
   test: