ci(build): do not cancel-in-progress on push runs (#637)

The concurrency group is per-ref (github.workflow-github.ref). On master,
every merge is a push to the same ref, so back-to-back merges share one
group and cancel-in-progress kills the prior merge in-flight rollup before
it verifies green. #626 (concurrency-groups) bit the #617 web-static lane
exactly this way: the last completed master CI run (28692641464) shows
Web-static verify=cancelled while Windows x86_64=success.

Gate cancel-in-progress to non-push events only. PR churn (rapid re-pushes
to a PR ref) still de-dupes and sheds the shared-pool OOM load that #626
targeted; master/release/tag runs always run to completion so a merged SHA
is actually verified. Fenced to the concurrency block, no job changes.

Co-authored-by: frstrtr <frstrtr@users.noreply.github.com>

Author: frstrtr

.github/workflows/build.yml

@@ -13,7 +13,11 @@ on:
 # distinct PRs/branches never cancel each other.
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
+  # Only cancel superseded PR runs; NEVER cancel a push (master/release/tag)
+  # run - back-to-back merges to master share this ref-group, so cancel-on-push
+  # would kill a merged SHA in-flight rollup before it verifies green (#626
+  # bit the #617 web-static lane exactly this way). PR churn still de-dupes.
+  cancel-in-progress: ${{ github.event_name != 'push' }}
 
 
 jobs: