[llvm] workflows/subscriber: Use github-automation container (PR #202777)

[Tom Stellard via llvm-commits]

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@@ -67,7 +57,7 @@ jobs:
               exit 1
               ;;
           esac
-          python3 ./github-automation.py \
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tstellar wrote:

I've installed the script to /usr/local/bin/, so I would need to do something like `python3 /usr/local/bin/github-automation.py` to run it.

https://github.com/llvm/llvm-project/pull/202777