treewide: bump to bazel 8

Change-Id: I18b6b4a5893167d722bb6270f11da1814c1664e3
Reviewed-on: https://review.monogon.dev/c/monogon/+/3963
Tested-by: Jenkins CI
Reviewed-by: Leopold Schabel <leo@monogon.tech>
diff --git a/.bazelversion b/.bazelversion
index 815da58..da15618 100644
--- a/.bazelversion
+++ b/.bazelversion
@@ -1 +1 @@
-7.4.1
+8.1.0
\ No newline at end of file