[llvm] Add Scorecard Action (PR #69933)

[Diogo Teles Sant'Anna via llvm-commits]

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+# This workflow uses actions that are not certified by GitHub. They are provided
+# by a third-party and are governed by separate terms of service, privacy
+# policy, and support documentation.
+
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diogoteles08 wrote:

Of course!

Additionally, we also have a [Scorecard badge](https://openssf.org/blog/2022/09/08/show-off-your-security-score-announcing-scorecards-badges/) that you can make more easily accessible in your README. I'd also happy to add this if you agree.

https://github.com/llvm/llvm-project/pull/69933