Bump actions/checkout from 3 to 4 (#786)

Author: dependabot[bot]

.github/workflows/html-macos.yml

@@ -8,7 +8,7 @@ jobs:
     runs-on: macos-latest
     steps:
     - name: Clone repo
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         fetch-depth: 0
     - name: Install pandoc

.github/workflows/linkcheck.yml

@@ -9,7 +9,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Clone repo
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
       with:
         fetch-depth: 0
     - name: Install pandoc