Quote the WhatsApp to.phone example in the Messages API

Unquoted, `+5547999998888` is parsed by YAML as an integer, so the rendered
example and the generated SDKs show the phone as a JSON number instead of a
string.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Author: csdinos

descriptions/0/api.intercom.io.yaml

@@ -21949,7 +21949,7 @@ paths:
                     type: admin
                     id: '991267817'
                   to:
-                    phone: +5547999998888
+                    phone: "+5547999998888"
                     name: John Doe
                   message_type: whatsapp
                   components:

descriptions/2.16/api.intercom.io.yaml

@@ -17380,7 +17380,7 @@ paths:
                     type: admin
                     id: '991267817'
                   to:
-                    phone: +5547999998888
+                    phone: "+5547999998888"
                     name: John Doe
                   message_type: whatsapp
                   components:

descriptions/2.17/api.intercom.io.yaml

@@ -19874,7 +19874,7 @@ paths:
                     type: admin
                     id: '991267817'
                   to:
-                    phone: +5547999998888
+                    phone: "+5547999998888"
                     name: John Doe
                   message_type: whatsapp
                   components: