test: adjust test-push-race.t timeout's to overall test timeout

The generic `tests/testlib/wait-on-file` mechanism scale its timeout with the
value of `HGTEST_TIMEOUT`, the `delaypush.py` in `test-push-race.t` is not doing
this, and we have been seeing more and more timeout from loaded CI worker
lately.

Adding this timeout scaling should help with that.

tests/test-push-race.t

@@ -48,6 +48,14 b' A set of extension and shell functions e'
   >     if watchpath is not None:
   >         ui.status(b'waiting on: %s\n' % watchpath)
   >         limit = 100
+  >         test_default_timeout = os.environ.get('HGTEST_TIMEOUT_DEFAULT')
+  >         test_timeout = os.environ.get('HGTEST_TIMEOUT')
+  >         if (
+  >             test_default_timeout is not None
+  >             and test_timeout is not None
+  >             and test_default_timeout < test_timeout
+  >         ):
+  >             limit = int(limit * (test_timeout / test_default_timeout))
   >         while 0 < limit and not os.path.exists(watchpath):
   >             limit -= 1
   >             time.sleep(0.1)