Add 'v261' branch to build workflow triggers

Author: srwi

.github/workflows/build.yml

@@ -16,7 +16,7 @@ name: Build
 on:
   # Trigger the workflow on pushes to only the 'main' branch (this avoids duplicate checks being run e.g., for dependabot pull requests)
   push:
-    branches: [ main ]
+    branches: [ main, v261 ]
   # Trigger the workflow on any pull request
   pull_request: