Disable slang-server for verilog extension (#40442)

Should be merged with
https://github.com/zed-industries/extensions/pull/3584, which adds
`slang-server` as a new language server, but should be disabled by
default due to an issue with it not initializing on Windows and being a
relatively new language server in general.

Release Notes:

- N/A

assets/settings/default.json

@@ -1820,6 +1820,7 @@
     },
     "SystemVerilog": {
       "format_on_save": "off",
+      "language_servers": ["!slang", "..."],
       "use_on_type_format": false
     },
     "Vue.js": {