chore(git): fix diagnostics

lua/git/object.lua

@@ -184,6 +184,7 @@ function M.read_uri(buf)
     vim.bo[buf].swapfile = false
     vim.bo[buf].bufhidden = "wipe"
 
+    ---@type string?
     local stdout = pending_content[buf]
     pending_content[buf] = nil
     if stdout == nil then