Also run only one browser tests job per ref

Author: pabzm

.github/workflows/browser_tests.yml

@@ -4,6 +4,10 @@ on:
   push:
   pull_request:
 
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
 permissions:
   contents: read