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

lua/git/util.lua

@@ -31,7 +31,10 @@ end
 function M.parse_revspec(revspec)
     local stage, path = revspec:match("^:([0123]):(.+)$")
     if stage then
-        return { stage = tonumber(stage), path = path }
+        return {
+            stage = tonumber(stage) --[[@as (0|1|2|3)?]],
+            path = path,
+        }
     end
     path = revspec:match("^:([^:]+)$")
     if path then