CI (Buildkite): temporarily allow the llvmpasses job to fail (#43663)

Author: DilumAluthge

.buildkite/pipelines/main/misc/llvmpasses.yml

@@ -26,6 +26,7 @@ steps:
     timeout_in_minutes: 60
   - label: "llvmpasses"
     key: "llvmpasses"
+    soft_fail: true # TODO: delete this line
     plugins:
       - JuliaCI/julia#v1:
           # Drop default "registries" directory, so it is not persisted from execution to execution