Bump actions/checkout from 3 to 4 (#783)

Author: dependabot[bot]

.github/workflows/docs.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: README.org -> README.md
         uses: docker://pandoc/core:2.9

.github/workflows/test.yml

@@ -27,7 +27,7 @@ jobs:
             experimental: true
 
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
 
       - uses: jcs090218/setup-emacs@master
         with: