patch 8.2.1631: test_fails() does not check the context of the line number

Problem:    test_fails() does not check the context of the line number.
Solution:   Use another argument to specify the context of the line number.
diff --git a/src/globals.h b/src/globals.h
index 6434190..337c068 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -224,6 +224,7 @@
 EXTERN int	emsg_assert_fails_used INIT(= FALSE);
 EXTERN char_u	*emsg_assert_fails_msg INIT(= NULL);
 EXTERN long	emsg_assert_fails_lnum INIT(= 0);
+EXTERN char_u	*emsg_assert_fails_context INIT(= NULL);
 
 EXTERN int	did_endif INIT(= FALSE);    // just had ":endif"
 #endif