patch 8.2.0028: searchpairpos() is not tested

Problem:    Searchpairpos() is not tested.
Solution:   Add tests.  Also improve searchpair() testing. (Dominique Pelle,
            closes #5388)
diff --git a/src/version.c b/src/version.c
index c3e900d..ec5c7b4 100644
--- a/src/version.c
+++ b/src/version.c
@@ -743,6 +743,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    28,
+/**/
     27,
 /**/
     26,