Fix flaky postgres tests (#5340)

* Use file lock for serial tests

* Add missing serial annotation

Author: rdettai

quickwit/Cargo.lock

@@ -52,7 +52,7 @@ futures = { workspace = true }
 md5 = { workspace = true }
 mockall = { workspace = true }
 rand = { workspace = true }
-serial_test = "3.1.0"
+serial_test = { version = "3.1.1", features = ["file_locks"] }
 tempfile = { workspace = true }
 tracing-subscriber = { workspace = true }