patch 8.1.1796: :argdo is not tested

Problem:    :argdo is not tested
Solution:   Add a test.
diff --git a/src/testdir/test_arglist.vim b/src/testdir/test_arglist.vim
index f161d6e..fc086fa 100644
--- a/src/testdir/test_arglist.vim
+++ b/src/testdir/test_arglist.vim
@@ -496,3 +496,12 @@
   exe 'argadd ' .repeat('x', &columns)
   args
 endfunc
+
+func Test_argdo()
+  next! Xa.c Xb.c Xc.c
+  new
+  let l = []
+  argdo call add(l, expand('%'))
+  call assert_equal(['Xa.c', 'Xb.c', 'Xc.c'], l)
+  bwipe Xa.c Xb.c Xc.c
+endfunc
diff --git a/src/version.c b/src/version.c
index 10e05f4..2b91490 100644
--- a/src/version.c
+++ b/src/version.c
@@ -774,6 +774,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1796,
+/**/
     1795,
 /**/
     1794,