ci: pin image versions used in CI so it remains deterministic (#28779)

We shouldn't use image versions in CI that can update all willy-nilly.
This will result in non-deterministic test runs.

`ubuntu-2404:2024.05.1` is currently the same as `ubuntu-2404:2024.05.1`
(see
https://discuss.circleci.com/t/new-ubuntu-24-04-linux-machine-executor-image/51018#linux-1)

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.circleci/config.yml

@@ -15,7 +15,7 @@ executors:
       NODE_OPTIONS: --max_old_space_size=3072
   node-linux-medium:
     machine:
-      image: ubuntu-2404:current
+      image: ubuntu-2404:2024.05.1
     resource_class: medium #// linux medium: 2 CPUs, 7.5 GB RAM, 10 credits/min
     environment:
       NODE_OPTIONS: --max_old_space_size=6144