patch 8.1.1466: not updating priority on existing sign

Problem:    Not updating priority on existing sign.
Solution:   Set the sign priority.  Add a test. (Yegappan Lakshmanan)
diff --git a/src/testdir/test_signs.vim b/src/testdir/test_signs.vim
index 426998d..a986e12 100644
--- a/src/testdir/test_signs.vim
+++ b/src/testdir/test_signs.vim
@@ -1183,6 +1183,24 @@
 	      \ 'priority' : 10}],
 	      \ s[0].signs)
 
+  " Place multiple signs with same id on a line with different priority
+  call sign_place(1, '', 'sign1', 'Xsign',
+	      \ {'lnum' : 5, 'priority' : 20})
+  call sign_place(1, '', 'sign2', 'Xsign',
+	      \ {'lnum' : 5, 'priority' : 10})
+  let s = sign_getplaced('Xsign', {'lnum' : 5})
+  call assert_equal([
+	      \ {'id' : 1, 'name' : 'sign2', 'lnum' : 5, 'group' : '',
+	      \ 'priority' : 10}],
+	      \ s[0].signs)
+  call sign_place(1, '', 'sign2', 'Xsign',
+	      \ {'lnum' : 5, 'priority' : 5})
+  let s = sign_getplaced('Xsign', {'lnum' : 5})
+  call assert_equal([
+	      \ {'id' : 1, 'name' : 'sign2', 'lnum' : 5, 'group' : '',
+	      \ 'priority' : 5}],
+	      \ s[0].signs)
+
   " Error case
   call assert_fails("call sign_place(1, 'g1', 'sign1', 'Xsign',
 	      \ [])", 'E715:')