Linkcheck fix (#3452)

## Issue Addressed

I think we're running into this in our linkcheck, so I'm going to frist verify linkcheck fails on the current version, and then try downgrading it to see if it passes chronotope/chrono#755

Co-authored-by: realbigsean <sean@sigmaprime.io>

.github/workflows/linkcheck.yml

@@ -21,7 +21,7 @@ jobs:
         run: docker network create book
 
       - name: Run mdbook server
-        run: docker run -v ${{ github.workspace }}/book:/book --network book --name book -p 3000:3000 -d peaceiris/mdbook:latest serve --hostname 0.0.0.0
+        run: docker run -v ${{ github.workspace }}/book:/book --network book --name book -p 3000:3000 -d peaceiris/mdbook:v0.4.20-rust serve --hostname 0.0.0.0
 
       - name: Print logs
         run: docker logs book