Use fixed path and fix path for HLint configuration.

The paths are passed as is to HLint, which does not use them as file patterns.  I.e., HLint uses a path to a specific directory or file, not a file pattern.

Author: chungyc

.github/workflows/hlint.yml

@@ -3,12 +3,12 @@ name: HLint
 on:
   push:
     paths:
-      - '**/site.hs'
+      - 'message-index/site.hs'
     branches:
       - main
   pull_request:
     paths:
-      - '**/site.hs'
+      - 'message-index/site.hs'
     types:
       - opened
       - synchronize
@@ -24,5 +24,5 @@ jobs:
       uses: haskell-actions/hlint-scan@v1
       with:
         path: |
-          **/site.hs
-        hints: message_index/.hlint.yml
+          message-index/site.hs
+        hints: message-index/.hlint.yml