patch 8.2.2561: not all textprop code is covered by tests

Problem:    Not all textprop code is covered by tests.
Solution:   Add a few more test cases. (Dominique Pellé, closes #7908)
diff --git a/src/version.c b/src/version.c
index 7f1e818..17cb8d9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2561,
+/**/
     2560,
 /**/
     2559,