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;

test/string/str2.c

@@ -1,8 +1,7 @@
 #include <assert.h>
+#include <myclib/mystring.h>
 #include <string.h>
 
-#include "../../string/mystring.h"
-
 void test_str2(void) {
 	string_s *s1 = string_new("Hello, world!", 0);
 	assert(s1 != NULL);

test/string/str3.c

@@ -1,8 +1,7 @@
 #include <assert.h>
+#include <myclib/mystring.h>
 #include <string.h>
 
-#include "../../string/mystring.h"
-
 void test_str3(void) {
 	/* Make a new string from format */
 	string_s *s = string_format("My name is %s (%d)", "John", 21);