fix(git): small bug fixes

lua/git/status_win.lua

@@ -311,6 +311,10 @@ local function render(bufnr, branch, groups)
         })
     end
     state[bufnr].lines = meta
+    -- The diff windows we last opened may now be showing content for an
+    -- entry whose underlying file has changed. Drop the cache so the next
+    -- show_diff recomputes pre/post panes instead of short-circuiting.
+    state[bufnr].last_shown_key = nil
 end
 
 ---@param bufnr integer