patch 8.1.0505: filter command test may fail if helplang is not set

Problem:    Filter command test may fail if helplang is not set.
Solution:   Set 'helplang' for the test. (James McCoy, closes #3591)
diff --git a/src/version.c b/src/version.c
index 2c06a0f..5da6027 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    505,
+/**/
     504,
 /**/
     503,