TST: Fix integer ops comparison test
The `op(Series[integer], other)` path was being tested twice.
The `op(IntegerArray, other)` path was not being tested.

Closes https://github.com/pandas-dev/pandas/issues/22096
Hello @TomAugspurger! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/tests/arrays/test_integer.py`](https://github.com/TomAugspurger/pandas/blob/dee6c8c7e63decbdb908fdaa255a430ca067cadf/pandas/tests/arrays/test_integer.py) !

 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23619?src=pr&el=h1) Report
> Merging [#23619](https://codecov.io/gh/pandas-dev/pandas/pull/23619?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/8ed92efc65b51a9010bd14e0e666fc722226e50a?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23619/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23619?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #23619   +/-   ##
=======================================
  Coverage   92.25%   92.25%           
=======================================
  Files         161      161           
  Lines       51277    51277           
=======================================
  Hits        47305    47305           
  Misses       3972     3972
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.63% <ø> (ø)` | :arrow_up: |
| #single | `42.32% <ø> (ø)` | :arrow_up: |


------

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 thanks @TomAugspurger 

do we have coverage for this anywhere else?

```
diff --git a/pandas/tests/arrays/test_integer.py b/pandas/tests/arrays/test_integer.py
index 51cd139a6..5e863f61c 100644
--- a/pandas/tests/arrays/test_integer.py
+++ b/pandas/tests/arrays/test_integer.py
@@ -347,6 +347,11 @@ class TestComparisonOps(BaseOpsUtil):
         other = pd.Series([0] * len(data))
         self._compare_other(data, op_name, other)
 
+    def test_compare_ndarray(self, data, all_compare_operators):
+        op_name = all_compare_operators
+        other = np.array(pd.Series([0] * len(data)))
+        self._compare_other(data, op_name, other)
+
 
 class TestCasting(object):
     pass
```

should we make these ops tests more general? (e.g. i think only integer na exercises them now, but in the future would be nice to automatically test). We have an open issue for writing base tests comparing arrays to `{scalar, list, ndarary, series, index}`