TST: Move a call out of an assert in the standard error rounding test

CodeQL reported py/side-effect-in-assert for the call to np.delete inside the
assert of test_std_errors_not_changed. np.delete returns a copy, so there was
no side effect, but the call is now made before the assert.

Author: bashtage

linearmodels/tests/asset_pricing/test_std_errors_rounding.py

@@ -86,7 +86,8 @@ def test_std_errors_not_changed():
     cov[2, 2] = np.nan
     se = _std_errors(cov)
     assert np.isnan(se[2])
-    assert np.all(np.isfinite(np.delete(se, 2)))
+    others = np.delete(se, 2)
+    assert np.all(np.isfinite(others))
 
 
 @pytest.mark.parametrize("risk_free", [False, True])