patch 8.2.0281: two placed signs in the same line are not combined

Problem:    Two placed signs in the same line are not combined.  E.g. in the
            terminal debugger a breakpoint and the PC cannot be both be
            displayed.
Solution:   Combine the sign column and line highlight attributes.
diff --git a/src/testdir/test_signs.vim b/src/testdir/test_signs.vim
index d480671..ce122e8 100644
--- a/src/testdir/test_signs.vim
+++ b/src/testdir/test_signs.vim
@@ -1742,6 +1742,7 @@
 	call setline(1, [repeat('x', 75), 'mmmm', 'yyyy'])
 	call cursor(2,1)
    	sign define s1 texthl=Search text==>
+   	sign define s2 linehl=Pmenu
 	redraw
    	sign place 10 line=2 name=s1
   END
@@ -1753,11 +1754,15 @@
   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>")
+  " Also place a line HL sign
+  call term_sendkeys(buf, ":sign place 11 line=2 name=s2\<CR>")
   call VerifyScreenDump(buf, 'Test_sign_cursor_3', {})
 
+  " update cursor position calculation
+  call term_sendkeys(buf, "lh")
+  call term_sendkeys(buf, ":sign unplace 11\<CR>")
+  call term_sendkeys(buf, ":sign unplace 10\<CR>")
+  call VerifyScreenDump(buf, 'Test_sign_cursor_4', {})
 
   " clean up
   call StopVimInTerminal(buf)