patch 9.0.1278: go.work.sum files are not recognized

Problem:    go.work.sum files are not recognized.
Solution:   Recognize go.work.sum files as the gosum filetype. (Amaan Qureshi,
            closes #11940)
diff --git a/src/version.c b/src/version.c
index 0768881..f21013d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1278,
+/**/
     1277,
 /**/
     1276,