Bump actions/checkout from 5 to 6 (#21)

Author: dependabot[bot]

.github/workflows/test.yml

@@ -40,7 +40,7 @@ jobs:
             emacs-version: 27.2
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - uses: jcs090218/setup-emacs@master
       with: