Update key

Author: marxin

.github/workflows/ci.yml

@@ -41,7 +41,7 @@ jobs:
         uses: actions/cache/restore@v4
         with:
           path: book/linkcheck/cache.json
-          key: linkcheck
+          key: linkcheck--${{ env.MDBOOK_LINKCHECK2_VERSION }}
 
       - name: Install latest nightly Rust toolchain
         if: steps.mdbook-cache.outputs.cache-hit != 'true'
@@ -58,7 +58,7 @@ jobs:
           cargo install mdbook-mermaid --version ${{ env.MDBOOK_MERMAID_VERSION }}
 
       - name: Check build
-        run: mdbook build
+        run: ENABLE_LINKCHECK=1 mdbook build
         continue-on-error: true
 
       - name: Save cached Linkcheck
@@ -67,7 +67,7 @@ jobs:
         uses: actions/cache/save@v4
         with:
           path: book/linkcheck/cache.json
-          key: linkcheck
+          key: linkcheck--${{ env.MDBOOK_LINKCHECK2_VERSION }}
 
       - name: Deploy to gh-pages
         if: github.event_name == 'push'