WORKSPACE: bump kernel to 5.15.104

Bumps the kernel to the latest patch release.

Hash verified against GPG signature from
647F28654894E3BD457199BE38DBBDC86092693E alias Greg KH.

Change-Id: I20d78d0492d1e869d684a1c045341f142f2039c8
Reviewed-on: https://review.monogon.dev/c/monogon/+/1410
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 2ef9ae6..236f891 100644
--- a/third_party/linux/external.bzl
+++ b/third_party/linux/external.bzl
@@ -23,6 +23,7 @@
         "5.10.4": "904e396c26e9992a16cd1cc989460171536bed7739bf36049f6eb020ee5d56ec",
         "5.15.2": "5634033a4981be42d3259f50d5371a2cdc9ace5d9860da67a2879630533ab175",
         "5.15.32": "1463cdfa223088610dd65d3eadeffa44ec49746091b8ae8ddac6f3070d17df86",
+        "5.15.104": "71c532ce09992e470f3259ffeb38d2b5bba990c243a559e4726a57412bd36b54",
     }
     http_archive(
         name = name,