checkout: add sparse-checkout-cone-mode passthrough

Required when sparse-checkout patterns include files (not just dirs) —
lint-github-docs uses cone-mode=false to pin package.json, pnpm-lock.yaml
etc. Without the passthrough actions/checkout treats files as dirs.

checkout/action.yml

@@ -13,6 +13,10 @@ inputs:
     description: 'Newline-separated sparse-checkout patterns. When set, the GCS cache is bypassed entirely and the step is a plain actions/checkout — avoids polluting the full-tree cache with sparse trees.'
     required: false
     default: ''
+  sparse-checkout-cone-mode:
+    description: 'Whether sparse-checkout patterns are cone-mode (true) or full patterns (false). Required as "false" when patterns include files, not just directories.'
+    required: false
+    default: 'true'
   ref:
     description: 'Branch, tag or SHA to check out on cache miss. Defaults to the workflow ref.'
     required: false
@@ -49,6 +53,7 @@ runs:
         fetch-depth: ${{ inputs.fetch-depth }}
         filter: ${{ inputs.filter }}
         sparse-checkout: ${{ inputs.sparse-checkout }}
+        sparse-checkout-cone-mode: ${{ inputs.sparse-checkout-cone-mode }}
         ref: ${{ inputs.ref }}
 
     - name: Strip credentials before caching