treewide: bump bazel to 8.3.1

This also bumps bazel_skylib, as it uses deprecated functionality.

Change-Id: I26d665967c14e5b3a437a3322f065ae1e2e63d9e
Reviewed-on: https://review.monogon.dev/c/monogon/+/4383
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/.bazelrc b/.bazelrc
index b3bbfde..ddef26c 100644
--- a/.bazelrc
+++ b/.bazelrc
@@ -134,7 +134,7 @@
 # Assume a 10k IOPS device (average NVMe) and 64GiB of RAM for test scheduling.
 test --local_resources=iops=10000 --local_resources=ram=64000
 
-common --experimental_downloader_config=build/bazel/bazel_downloader.cfg
+common --downloader_config=build/bazel/bazel_downloader.cfg
 
 # Load custom per-user settings.
 try-import %workspace%/.bazelrc.user