fix(ci): retry the docs push after a rejected ref

Several releases push casks to this tap at the same time. The docs job then
pushed on top of a ref that had moved, and GitHub rejected it with "cannot
lock ref". The job now rebases and retries. If the rebase fails it resets to
the remote, regenerates the page and pushes again. A concurrency group keeps
two docs runs from overlapping.

.github/workflows/docs.yml

@@ -16,6 +16,10 @@ permissions:
   pages: write
   id-token: write
 
+concurrency:
+  group: update-docs
+  cancel-in-progress: false
+
 jobs:
   update-docs:
     runs-on: ubuntu-latest
@@ -46,7 +50,22 @@ jobs:
           git config --local user.name "github-actions[bot]"
           git add docs/
           git commit -m "docs: auto-update documentation from casks"
-          git push
+          for attempt in 1 2 3 4; do
+            if git pull --rebase origin main; then
+              git push && exit 0
+            else
+              git rebase --abort || true
+              git reset --hard origin/main
+              ./scripts/generate-docs.sh
+              git diff --quiet docs/index.html && exit 0
+              git add docs/
+              git commit -m "docs: auto-update documentation from casks"
+              git push && exit 0
+            fi
+            sleep $((attempt * 5))
+          done
+          echo "could not push after 4 attempts" >&2
+          exit 1
 
   deploy-pages:
     needs: update-docs