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.

src/vim.h

@@ -2030,6 +2030,7 @@ typedef int sock_T;
 #define VAR_TYPE_JOB	    8
 #define VAR_TYPE_CHANNEL    9
 #define VAR_TYPE_BLOB	    10
+#define VAR_TYPE_INSTR	    11
 
 #define DICT_MAXNEST 100	// maximum nesting of lists and dicts