Switch to 1.12 for benchmarks

[only benchmarks]

Author: christiangnrd

.buildkite/pipeline.yml

@@ -415,7 +415,7 @@ steps:
   - label: ":racehorse: Benchmarks"
     plugins:
       - JuliaCI/julia#v1:
-          version: "1.11"
+          version: "1.12"
     command: |
       julia --project=perf -e '
         using Pkg