ci: work around temperamental kroki API

The build step performs requests against kroki.io, which are notoriously
flaky. We'll now retry this step up to three times and only then assume
something is actually wrong, rather than reporting failure due to a
temperamental API.

Signed-off-by: Luca Zeuch <[email protected]>

Author: l-zeuch

.github/workflows/hugo.yml

@@ -45,8 +45,15 @@ jobs:
         run: |
           [[ -f package-lock.json || -f npm-shrinkwrap.json ]] && npm ci || true
 
+      # The website builds are notoriously flaky; specifically, Kroki tends to return
+      # a "Bad Request" error for no apparent reason. We will retry up to 3 times and then
+      # assume that the build is actually broken, rather than temperamental.
       - name: Build website
-        run: npm run build
+        uses: nick-fields/retry@v3
+        with:
+          retry_on: error
+          max_attempts: 3
+          command: npm run build
 
       - name: Setup Pages
         if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/master' }}