fix(providers): Ensure working on nvim-0.7

This commit removed the ability to receive symbols from all attached
clients in the current buffer. Everything works as before when only one
client is attached to a buffer.

This also fixes outline LSP finding clients on nvim-0.7

lua/outline/providers/init.lua

@@ -1,17 +1,19 @@
 local M = {}
 local import_prefix = 'outline/providers/'
 
----@return outline.Provider?
+---@return outline.Provider?, table?
 function M.find_provider()
   if not M.providers then
     M.providers = vim.tbl_map(function(p)
       return import_prefix .. p
     end, require('outline.config').get_providers())
   end
+
   for _, path in ipairs(M.providers) do
     local provider = require(path)
-    if provider.supports_buffer(0) then
-      return provider
+    local ok, info = provider.supports_buffer(0)
+    if ok then
+      return provider, info
     end
   end
 end