Move amd64 arch builds to self hosted runners

Our self hosted runners are cheaper and faster so we want to move to
them. Unfortunately, we do not have arm based runners so keep those on
Github hosted runners.

Author: tgxworld

.github/workflows/build.yml

@@ -27,18 +27,18 @@ jobs:
           echo "timestamp=$timestamp" >> $GITHUB_OUTPUT
 
   base:
-    # `unbuntu-22.04-8core` for arch amd64 non-scheduled builds
-    # `unbuntu-22.04` for arch amd64 scheduled builds
+    # `debian-12` for amd64 builds
     # `unbuntu-22.04-8core-arm` for arch arm64 non-scheduled builds
     # `unbuntu-22.04-2core-arm` for arch arm64 scheduled builds
-    runs-on: ubuntu-22.04${{ ((github.event_name != 'schedule') && '-8core') || (( matrix.arch == 'arm64' && '-2core' ) || '') }}${{ (matrix.arch == 'arm64') && '-arm' || '' }}
+    runs-on: ${{ (matrix.arch == 'amd64' && 'debian-12') || (github.event_name == 'schedule' && 'ubuntu-22.04-2core-arm') || 'ubuntu-22.04-8core-arm' }}
     strategy:
       matrix:
         arch: [amd64, arm64]
     timeout-minutes: ${{ (github.event_name == 'schedule' && 90) || ((matrix.arch == 'arm64' && 45) || 30) }}
     needs: timestamp
     env:
       TIMESTAMP: ${{ needs.timestamp.outputs.timestamp }}
+    container: discourse/ruby:3.3-bookworm-slim
     services:
       registry:
         image: registry:2