patch 8.2.0575: :digraph! not tested

Problem:    :digraph! not tested.
Solution:   Add a test. (Dominique Pelle, closes #5925)

src/testdir/test_digraph.vim

@@ -434,6 +434,18 @@ func Test_digraphs_output()
   call assert_equal('Z% Ж  1046',  matchstr(out, '\C\<Z%\D*1046\>'))
   call assert_equal('u- ū  363',   matchstr(out, '\C\<u-\D*363\>'))
   call assert_equal('SH ^A   1',   matchstr(out, '\C\<SH\D*1\>'))
+  call assert_notmatch('Latin supplement', out)
+
+  let out_bang_without_custom = execute(':digraph!')
+  digraph lt 60
+  let out_bang_with_custom = execute(':digraph!')
+  call assert_notmatch('lt', out_bang_without_custom)
+  call assert_match("^\n"
+        \        .. "NU ^@  10 .*\n"
+        \        .. "Latin supplement\n"
+        \        .. "!I ¡  161 .*\n"
+        \        .. ".*\n"
+        \        .. 'Custom\n.*\<lt <   60\>', out_bang_with_custom)
   bw!
 endfunc
 

src/version.c

@@ -746,6 +746,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    575,
 /**/
     574,
 /**/