Improve support of display-line-numbers in package.el

* lisp/emacs-lisp/package.el (package-menu--refresh): Redisplay
the header.  (Bug#27895)
* lisp/emacs-lisp/tabulated-list.el
(tabulated-list-line-number-width): Fix the case when
display-line-numbers is nil.

lisp/emacs-lisp/package.el

@@ -2751,6 +2751,7 @@ KEYWORDS should be nil or a list of keywords."
               (push pkg info-list))))))
 
     ;; Print the result.
+    (tabulated-list-init-header)
     (setq tabulated-list-entries
           (mapcar #'package-menu--print-info-simple info-list))))
 

lisp/emacs-lisp/tabulated-list.el

@@ -191,11 +191,13 @@ Populated by `tabulated-list-init-header'.")
   ;; line-number-display-width returns the value for the selected
   ;; window, which might not be the window in which the current buffer
   ;; is displayed.
-  (let ((cbuf-window (get-buffer-window (current-buffer))))
-    (if (window-live-p cbuf-window)
-        (with-selected-window cbuf-window
-          (+ (line-number-display-width) 2))
-      (if display-line-numbers 4 0))))
+  (if (not display-line-numbers)
+           0
+    (let ((cbuf-window (get-buffer-window (current-buffer))))
+      (if (window-live-p cbuf-window)
+          (with-selected-window cbuf-window
+            (+ (line-number-display-width) 2))
+        4))))
 
 (defun tabulated-list-init-header ()
   "Set up header line for the Tabulated List buffer."