When running tests on CI, I hit a race condition which caused the `ExtensionManagerTests::test_install_media_concurrent_threads` test to fail. The version check in `install_extension_media()` happened only before acquiring the lock file. If one thread completed the install and released the lock before another thread attempted to acquire it, the second thread would successfully lock and redundantly reinstall, since its local old_version was already stale. This change makes us re-check the installed version after acquiring the lock to skip the install if another thread/process already completed it. Testing Done: Ran unit tests.