ci: use new buildbot worker images with Debian 11

Debian 10 LTS support ends on 6/2024, so it makes no sense to use it as
a base for 23.05 release, so lets switch to Debian 11 which should've
LTS support till 6/2026.

References: f2744543fa
Signed-off-by: Petr Štetiar <ynezz@true.cz>

.github/workflows/Dockerfile.tools

@@ -1,4 +1,4 @@
-FROM registry.gitlab.com/openwrt/buildbot/buildworker-3.4.1
+FROM ghcr.io/openwrt/buildbot/buildworker-v3.8.0:v2
 
 COPY --chown=buildbot staging_dir/host /prebuilt_tools/staging_dir/host
 COPY --chown=buildbot build_dir/host /prebuilt_tools/build_dir/host

.github/workflows/build-tools.yml

@@ -13,7 +13,7 @@ jobs:
   build:
     name: Build tools
     runs-on: ubuntu-latest
-    container: registry.gitlab.com/openwrt/buildbot/buildworker-3.4.1
+    container: ghcr.io/openwrt/buildbot/buildworker-v3.8.0:v2
 
     steps:
       - name: Checkout