[llvm] [NFC][MLGO] Fix indentation in MLGO.rst (PR #146444)

[S. VenkataKeerthy via llvm-commits]

svkeerthy wrote:

### Merge activity

* **Jul 1, 12:59 AM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/146444).


https://github.com/llvm/llvm-project/pull/146444