Prepare release 1.17.0 (ocaml#1219)

* chore: restore lost version number in changes
     (erased in c8c1096)

* chore: bump version number in changes before release

CHANGES.md

@@ -1,4 +1,4 @@
-# Unreleased
+# 1.17.0
 
 ## Fixes
 
@@ -107,6 +107,8 @@
   [#941](https://github.com/ocaml/ocaml-lsp/issues/941),
   [#1003](https://github.com/ocaml/ocaml-lsp/issues/1003))
 
+# 1.15.0
+
 ## Features
 
 - Enable [semantic highlighting](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_semanticTokens)