perf(ci): add build cancel concurrency

Signed-off-by: skjnldsv <skjnldsv@protonmail.com>

Author: skjnldsv

.github/workflows/sphinxbuild.yml

@@ -10,6 +10,10 @@ on:
 permissions:
   contents: read
 
+concurrency:
+  group: build-documentation-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
 jobs:
   build: