Summary:
In the test, the tserver may crash (simulated with a gflag) before the newly appended log entry is synced, resulting in an empty rebuilt footer after the tserver restarts, causing the test to fail.
To fix this, ensure the entry is synced before restarting the tserver.
Jira: DB-15635

Test Plan: ./yb_build.sh release --cxx-test integration-tests_restart-test --gtest_filter RestartTest.WalFooterProperlyInitialized --clang17 -n 100

Reviewers: rthallam, bkolagani

Reviewed By: bkolagani

Subscribers: ybase

Differential Revision: https://phorge.dev.yugabyte.com/D42329