refactor(test): remove relative include

test/string/str1.c

@@ -1,10 +1,9 @@
 #include <assert.h>
+#include <myclib/mystring.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
-#include "../../string/mystring.h"
-
 void test_str1(void) {
 	size_t length;
 	size_t capacity;