ci(build): keep Web-static verify on GitHub-hosted (not self-hosted)

The self-hosted switch routed the sub-minute Web-static verify job onto the
c2pool-build Linux runner along with the heavy C++ lanes. The puppeteer
pixel-regression harness cannot complete page navigation there: page.goto
times out at 15s under both load and domcontentloaded waitUntil, because the
self-hosted runner environment never fires the navigation-complete event for
dashboard.html. The job is green on ubuntu-24.04 and gains nothing from the
32-core box, so pin it back to GitHub-hosted. Dashboard-owned web-static
assets and the visual harness are unchanged and not the cause.

Author: frstrtr

.github/workflows/build.yml

@@ -441,7 +441,10 @@ jobs:
   # ════════════════════════════════════════════════════════════════════════════
   web-static:
     name: Web-static verify
-    runs-on: ${{ (github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == github.repository) && fromJSON('["self-hosted","Linux","X64","c2pool-build"]') || 'ubuntu-24.04' }}
+    # Pin to GitHub-hosted: sub-minute JS job needs no self-hosted compute,
+    # and the puppeteer pixel harness cannot complete page navigation in the
+    # self-hosted runner env (DOMContentLoaded never fires within 15s).
+    runs-on: ubuntu-24.04
     defaults:
       run:
         working-directory: web-static/sharechain-explorer