t/{linux,-firmware}: fix Zenbleed (CVE-2023-20593)

This fixes the Zenbleed vulnerability by including the latest fixed
microcode from linux-firmware. They don't do proper release management
but just tag a date approximately every month to keep distros happy.
Thus we need to use a master commit to get the fixes now.

Also update Linux to 5.15.122 to make sure that we know in case the
microcode fix somehow didn't get applied.

Change-Id: I5e26826e6df0f665e1a23efe8587dfb93edb2d94
Reviewed-on: https://review.monogon.dev/c/monogon/+/1974
Reviewed-by: Leopold Schabel <leo@monogon.tech>
Tested-by: Jenkins CI
diff --git a/WORKSPACE b/WORKSPACE
index fb00bd9..c76fe4b 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -133,14 +133,14 @@
 
 linux_external(
     name = "linux",
-    version = "5.15.104",
+    version = "5.15.122",
 )
 
 load("//third_party/linux-firmware:external.bzl", "linux_firmware_external")
 
 linux_firmware_external(
     name = "linux-firmware",
-    version = "20230310",
+    version = "b6ea35ff6b9869470a0c68813f1668acb3d356a8",
 )
 
 load("//third_party/intel_ucode:external.bzl", "intel_ucode_external")