[3rdparty] Bump symfony to 4.2.3

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>

diff --git a/3rdparty b/3rdparty
index 7c64d231f833b8ab8f9dcd017499c8c18b7b78f9..3421f64a4312dc7a48a82cce9becd2cdf888caa4 160000 (submodule)
--- a/3rdparty
+++ b/3rdparty
@@ -1 +1 @@
-Subproject commit 7c64d231f833b8ab8f9dcd017499c8c18b7b78f9
+Subproject commit 3421f64a4312dc7a48a82cce9becd2cdf888caa4