patch 8.1.1488: summary of tests has incorrect failed count

Problem:    Summary of tests has incorrect failed count.
Solution:   Add to the failed count instead of setting it. (Christian Brabandt)
diff --git a/src/testdir/summarize.vim b/src/testdir/summarize.vim
index 5baee63..6944567 100644
--- a/src/testdir/summarize.vim
+++ b/src/testdir/summarize.vim
@@ -6,7 +6,7 @@
     if a:type ==# 'executed'
       let g:executed += (a:match+0)
     elseif a:type ==# 'failed'
-      let g:failed = a:match+0
+      let g:failed += a:match+0
     elseif a:type ==# 'skipped'
       let g:skipped += 1
       call extend(g:skipped_output, ["\t".a:match])
diff --git a/src/version.c b/src/version.c
index 5ac6f9d..90ee247 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1488,
+/**/
     1487,
 /**/
     1486,