patch 8.2.0108: when sign text is changed a manual redraw is needed

Problem:    When sign text is changed a manual redraw is needed. (Pontus
            Lietzler)
Solution:   Redraw automatically. (closes #5455)
diff --git a/src/testdir/test_signs.vim b/src/testdir/test_signs.vim
index 862199c..d480671 100644
--- a/src/testdir/test_signs.vim
+++ b/src/testdir/test_signs.vim
@@ -1747,12 +1747,16 @@
   END
   call writefile(lines, 'XtestSigncolumn')
   let buf = RunVimInTerminal('-S XtestSigncolumn', {'rows': 6})
-  call VerifyScreenDump(buf, 'Test_sign_cursor_01', {})
+  call VerifyScreenDump(buf, 'Test_sign_cursor_1', {})
+
+  " Change the sign text
+  call term_sendkeys(buf, ":sign define s1 text=-)\<CR>")
+  call VerifyScreenDump(buf, 'Test_sign_cursor_2', {})
 
   " update cursor position calculation
   call term_sendkeys(buf, "lh")
   call term_sendkeys(buf, ":sign unplace 10\<CR>")
-  call VerifyScreenDump(buf, 'Test_sign_cursor_02', {})
+  call VerifyScreenDump(buf, 'Test_sign_cursor_3', {})
 
 
   " clean up