trace2: fix up a missing "leave" entry point

Fix a trivial bug that's been here since the shared/do_write_index
tracing was added in 42fee7a3 ("trace2:data: add trace2
instrumentation to index read/write", 2019-02-22). We should have
enter/leave points, not two enter/enter points. This resulted in an
"enter" event without a corresponding "leave" event.
Signed-off-by: NÆvar Arnfjörð Bjarmason <avarab@gmail.com>
Acked-by: NDerrick Stolee <dstolee@microsoft.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

read-cache.c

@@ -3127,7 +3127,7 @@ static int write_shared_index(struct index_state *istate,
 	trace2_region_enter_printf("index", "shared/do_write_index",
 				   the_repository, "%s", (*temp)->filename.buf);
 	ret = do_write_index(si->base, *temp, 1);
-	trace2_region_enter_printf("index", "shared/do_write_index",
+	trace2_region_leave_printf("index", "shared/do_write_index",
 				   the_repository, "%s", (*temp)->filename.buf);
 
 	if (ret)