[llvm] [GitHub][workflows] Ask reviewers to merge PRs when author can not (PR #81142)

[Tom Stellard via llvm-commits]

================
@@ -0,0 +1,38 @@
+name: "Prompt reviewers to merge PRs on behalf of authors"
+
+permissions:
+  contents: read
+
+on:
+  pull_request_review:
+    types:
+      - submitted
+
+jobs:
+  merge_on_behalf_information_comment:
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tstellar wrote:

I think the convention is to use dashes instead of underscores here.

https://github.com/llvm/llvm-project/pull/81142