Treat *.ml{i} in Linguist as OCaml (#1828)

Summary:
A few files (see below) are being interpreted as SML; this corrects Linguist to treat them as OCaml.

<img width="889" alt="Screenshot 2024-04-01 at 16 34 37" src="https://github.com/facebook/infer/assets/1146876/cfc2911b-f5d5-4586-8440-56d77e6cbad2">

Pull Request resolved: #1828

Reviewed By: ngorogiannis

Differential Revision: D55634827

Pulled By: jvillard

fbshipit-source-id: 521cc54713c063ae3bb19100c22b839a4e2efadf

.gitattributes

@@ -1 +1,3 @@
 website/** linguist-documentation
+*.ml linguist-language=OCaml
+*.mli linguist-language=OCaml