Fix include path to point to test directory

The previous fix pointed -I to test/include, but the .vcl files
use paths like:
  .include "include/db_in_db_out.i"

When masp resolves includes with -I flag, it concatenates:
  include_path + "/" + file_from_include_directive

So with -I test/include, it would look for:
  test/include/include/db_in_db_out.i  (wrong - double "include")

Corrected to point -I to test/ directory, so it looks for:
  test/include/db_in_db_out.i  (correct!)

This matches how the .vcl files reference the includes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: fjtrujy

test/unit/test_stress_parallel.c

@@ -54,7 +54,8 @@ int main(void) {
     char include_path[1024];
 
     snprintf(masp_path, sizeof(masp_path), "%s/src/masp", BUILD_DIR);
-    snprintf(include_path, sizeof(include_path), "%s/test/include", SRC_DIR);
+    // Point to test/ directory so masp can resolve "include/*.i" paths
+    snprintf(include_path, sizeof(include_path), "%s/test", SRC_DIR);
 
     // Check if masp exists
     struct stat st;