ci: don't cancel docs build of other PRs.

PRs will only build the documentation and never publish it. Therefore,
these should run in parallel to check if the docs build and (to save
resources) they can cancel previous run when the PR is updated.

The main branch also publishes the docs. Then merging several PRs in
short succession the this workflow must be cancelled to avoid outdated
docs from being published.

Author: 1uc

.github/workflows/gh-pages.yml

@@ -16,7 +16,7 @@ permissions:
 
 # Allow only one concurrent deployment
 concurrency:
-  group: "pages"
+  group: ${{ github.workflow }}#${{ github.ref }}
   cancel-in-progress: true
 
 jobs: