test(file): fix a typo in a segment_io test name

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N4PmceDHg8rFe5bgkhGFU9
Signed-off-by: Claude <noreply@anthropic.com>

Author: claude

vortex-file/src/segment_io/tests.rs

@@ -255,7 +255,7 @@ async fn fetches_finished_at_submit_are_reported(#[case] segment: u32) -> Vortex
 }
 
 #[tokio::test]
-async fn one_sessions_announcement_widens_anothers_fetch() -> VortexResult<()> {
+async fn an_announcement_widens_another_sessions_fetch() -> VortexResult<()> {
     let (service, file, reader) = service(Arc::new(NoOpSegmentCache));
     let _announced = service
         .session()