patch 8.2.2842: Vim9: skip argument to searchpair() is not compiled

Problem:    Vim9: skip argument to searchpair() is not compiled.
Solution:   Add VAR_INSTR.
diff --git a/src/testing.c b/src/testing.c
index 7409237..cded3c7 100644
--- a/src/testing.c
+++ b/src/testing.c
@@ -1023,6 +1023,7 @@
 	case VAR_FLOAT:
 	case VAR_SPECIAL:
 	case VAR_STRING:
+	case VAR_INSTR:
 	    break;
 	case VAR_JOB:
 #ifdef FEAT_JOB_CHANNEL