linux: bump to 6.1.56

This gets us to the latest LTS kernel, 5.15 is nearly two years old.

Change-Id: I2f386c334b5067b9ced1b5286253d439884182bf
Reviewed-on: https://review.monogon.dev/c/monogon/+/2210
Tested-by: Jenkins CI
Reviewed-by: Tim Windelschmidt <tim@monogon.tech>
diff --git a/WORKSPACE b/WORKSPACE
index a2c972a..f5560cc 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -193,7 +193,7 @@
 
 linux_external(
     name = "linux",
-    version = "5.15.125",
+    version = "6.1.56",
 )
 
 load("//third_party/linux-firmware:external.bzl", "linux_firmware_external")