Add new tests to improve coverage stats

[vlad-perevezentsev]

This PR continues #2268 and #2272 and suggests adding a couple new tests to slightly improve code coverage stats

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[coveralls]

coverage: 71.289% (+0.01%) from 71.275%
when pulling f45cf8f on new_tests_coverage
into 0181564 on master.

[github-actions]

Array API standard conformance tests for dpnp=0.17.0dev5=py312he4f9c94_4 ran successfully.
Passed: 957
Failed: 0
Skipped: 43

[antonwolfy]

LGTM, thank you @vlad-perevezentsev

[antonwolfy]

both output arrays are dpnp.ndarray, so we no need to use assert util function from numpy here:

Suggested change

	expected = dpnp.matmul(a, b)
	assert_allclose(result, expected)
	expected = a @ b
	assert (result == expected).all()