Use a cache for lychee (#167)

.github/workflows/links.yml

@@ -12,10 +12,15 @@ jobs:
     - uses: actions/checkout@v4
       with:
         fetch-depth: 0
+    - uses: actions/cache@v4
+      with:
+        path: .lycheecache
+        key: cache-lychee-${{ github.sha }}
+        restore-keys: cache-lychee-
     - uses: lycheeverse/lychee-action@v1.9.3
       with:
+        fail: true
         args: >-
           -v -n "*.md" "**/*.md"
           --exclude "http://localhost*"
-    - name: fail for link errors
-      run: exit ${{ steps.lychee.outputs.exit_code }}
+          --max-concurrency 5 --cache --max-cache-age 1d