tests: Update submodule to the latest commit on libcgroup-tests main branch

Closes: https://github.com/libcgroup/libcgroup/issues/71
Reported-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>

diff --git a/tests b/tests
index 918443bd89efb807d92c1754b0b3fbff4bd3304f..3e786fc4c024662cc38c8a39868354c55465f487 160000 (submodule)
--- a/tests
+++ b/tests
@@ -1 +1 @@
-Subproject commit 918443bd89efb807d92c1754b0b3fbff4bd3304f
+Subproject commit 3e786fc4c024662cc38c8a39868354c55465f487