WORKSPACE: update linux to 6.6.42

Stable release bump, no significant changes expected.
No relevant regressions on the linux-regressions list.

Change-Id: I7688746eb94d514d53bfaa696ea5312a03b39690
Reviewed-on: https://review.monogon.dev/c/monogon/+/3254
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/third_party/linux/external.bzl b/third_party/linux/external.bzl
index 3edd217..548d192 100644
--- a/third_party/linux/external.bzl
+++ b/third_party/linux/external.bzl
@@ -20,6 +20,7 @@
     sums = {
         "6.6.13": "88b89e7dd41ead4e3ab1e411c8bb8d592575acf815cf1df3c0dc57e2e882c0bc",
         "6.6.30": "b66a5b863b0f8669448b74ca83bd641a856f164b29956e539bbcb5fdeeab9cc6",
+        "6.6.42": "8801c8c297d774e76044977ec3d0684399dc4e7cce347d730874ec78b774e683",
     }
     http_archive(
         name = name,