Add test for str function

Author: namannimmo10

integration_tests/test_builtin_str.py

@@ -1,6 +1,8 @@
 def test_str_int():
     s: str
-    s = str_int(356)
+    s = str(356)
     assert s == "356"
-    s = str_int(-567)
+    s = str(-567)
     assert s == "-567"
+    assert str(4) == "4"
+    assert str(-5) == "-5"