refactor: rename Plugin.lock => Plugin.pin to prevent confusion with the lockfile

lua/lazy/core/plugin.lua

@@ -32,7 +32,7 @@ M.dirty = false
 ---@field tag? string
 ---@field commit? string
 ---@field version? string
----@field lock? boolean
+---@field pin? boolean
 
 ---@class LazyPlugin: LazyPluginHandlers,LazyPluginHooks,LazyPluginRef
 ---@field [1] string

lua/lazy/manage/task/git.lua

@@ -131,7 +131,7 @@ M.checkout = {
 
     -- if the plugin is locked and we did not just clone it,
     -- then don't update
-    if self.plugin.lock and not self.plugin._.cloned then
+    if self.plugin.pin and not self.plugin._.cloned then
       target = info
     end