Bump actions/cache from 5 to 6 (#913)

Author: dependabot[bot]

.github/workflows/link-checker-prs.yml

@@ -29,7 +29,7 @@ jobs:
           echo "MARKDOWN_FILES=$md_files" >> $GITHUB_ENV
 
       - name: Restore lychee cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: .lycheecache
           key: cache-lychee-${{ github.sha }}

.github/workflows/link-checker.yml

@@ -18,7 +18,7 @@ jobs:
       - uses: actions/checkout@v7
 
       - name: Restore lychee cache
-        uses: actions/cache@v5
+        uses: actions/cache@v6
         with:
           path: .lycheecache
           key: cache-lychee-${{ github.sha }}