patch 8.2.4525: some GUI tests don't work on Athena

Problem:    Some GUI tests don't work on Athena.
Solution:   Skip tests that won't work. (Yegappan Lakshmanan, closes #9902)
diff --git a/src/testdir/test_gui.vim b/src/testdir/test_gui.vim
index ca81ffa..c2ce50d 100644
--- a/src/testdir/test_gui.vim
+++ b/src/testdir/test_gui.vim
@@ -1364,6 +1364,10 @@
 
 " Test for generating a GUI tabline event to select a tab page
 func Test_gui_tabline_event()
+  if has('gui_athena')
+    throw 'Skipped: tabline is not supported in Athena GUI'
+  endif
+
   %bw!
   edit Xfile1
   tabedit Xfile2
@@ -1391,6 +1395,9 @@
 
 " Test for generating a GUI tabline menu event to execute an action
 func Test_gui_tabmenu_event()
+  if has('gui_athena')
+    throw 'Skipped: tabmenu is not supported in Athena GUI'
+  endif
   %bw!
 
   " Try to close the last tab page
@@ -1427,6 +1434,11 @@
 
 " Test for find/replace text dialog event
 func Test_gui_findrepl()
+  " Find/Replace dialog is supported only on GTK, Motif and MS-Windows.
+  if !has('gui_gtk') && !has('gui_motif') && !has('gui_win32')
+    return
+  endif
+
   new
   call setline(1, ['one two one', 'Twoo One two oneo'])