bpo-37953: Fix deprecation warnings in test_typing (GH-16133)

bpo-37953: Fix deprecation warnings in test_typing (GH-16133)

self.assertEquals() is deprecated.

```
./python -We -m test test_typing
Run tests sequentially
0:00:00 load avg: 0.23 [1/1] test_typing
test test_typing failed -- Traceback (most recent call last):
  File "/home/lubuntu2/cpython/Lib/test/test_typing.py", line 2382, in test_forward_equality_gth
    self.assertEquals(Union[c1, c1_gth], Union[c1])
  File "/home/lubuntu2/cpython/Lib/unittest/case.py", line 1390, in deprecated_func
    warnings.warn(
DeprecationWarning: Please use assertEqual instead.

test_typing failed

== Tests result: FAILURE ==

1 test failed:
    test_typing

Total duration: 140 ms
Tests result: FAILURE
```

https://bugs.python.org/issue37953