[llvm] [CI] Add Github actions job to build LLVM documentation (PR #69269)

[Tom Stellard via llvm-commits]

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@@ -0,0 +1,43 @@
+# LLVM Documentation CI
+# Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+# See https://llvm.org/LICENSE.txt for license information.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+name: "Test documentation build"
+
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tstellar wrote:

```suggestion

permissions:
  contents: read
  
```

This is standard for all our workflow files.

https://github.com/llvm/llvm-project/pull/69269