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/testdir/test_filetype.vim b/src/testdir/test_filetype.vim
index 101bdfd..1f9aae6 100644
--- a/src/testdir/test_filetype.vim
+++ b/src/testdir/test_filetype.vim
@@ -233,7 +233,7 @@
     \ 'gnuplot': ['file.gpi', '.gnuplot'],
     \ 'go': ['file.go'],
     \ 'gomod': ['go.mod'],
-    \ 'gosum': ['go.sum'],
+    \ 'gosum': ['go.sum', 'go.work.sum'],
     \ 'gowork': ['go.work'],
     \ 'gp': ['file.gp', '.gprc'],
     \ 'gpg': ['/.gnupg/options', '/.gnupg/gpg.conf', '/usr/any/gnupg/options.skel', 'any/.gnupg/gpg.conf', 'any/.gnupg/options', 'any/usr/any/gnupg/options.skel'],
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,