ci(qt): cap Qt WebEngine leak gate at timeout-minutes: 20

The leak harness wraps the run in `timeout 180`, but QtWebEngine spawns
Chromium zygote/helper child processes that survive when timeout SIGTERMs
only the immediate child. The orphans keep the xvfb-run pipe open, so the
job hangs to the 360-min runner default instead of finishing. A job-level
timeout-minutes makes the runner force-kill the whole process tree, so a
hung gate costs ~20 min, not hours. continue-on-error semantics are
unchanged (gate stays advisory during Qt bring-up).

Author: frstrtr

.github/workflows/build.yml

@@ -302,6 +302,11 @@ jobs:
   qt-webengine:
     name: Qt WebEngine leak gate
     runs-on: ubuntu-24.04
+    # Hard ceiling: orphaned QtWebEngine/Chromium helper children survive
+    # the inner `timeout 180`, holding the xvfb pipe open and hanging the
+    # job to the 360-min runner default. Cap it so a hung leak gate is
+    # force-killed (with its whole process tree) in minutes, not hours.
+    timeout-minutes: 20
     steps:
       - uses: actions/checkout@v6