refactor(ops/pipelines): use large build slots for eval

Change-Id: I22b3ebb91695a3d43696196c0a189d3b1656df8d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/13128
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI
Autosubmit: tazjin <tazjin@tvl.su>

ops/pipelines/static-pipeline.yaml

@@ -49,9 +49,9 @@ steps:
   # Generate & upload dynamic build steps
   - label: ":llama:"
     key: "pipeline-gen"
-    concurrency_group: 'depot-nix-eval'
-    concurrency: 4 # TODO: limit per builder host?
     priority: 1
+    agents:
+        large: true
     command: |
       set -ue