Exclude headers with SYCL kernels from the coverage report

[antonwolfy]

The PR excludes the headers files under backend/kernels/elementwise_functions from the coverage report, because there is no way to cover structures used inside the SYCL kernels.

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[github-actions]

Array API standard conformance tests for dpnp=0.20.0dev0=py313h509198e_13 ran successfully.
Passed: 1227
Failed: 0
Skipped: 9

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/pull/2623/index.html

[coveralls]

coverage: 74.387% (+6.6%) from 67.791%
when pulling fea1842 on exclude-kernels-headers-from-default-coverage
into fc14877 on master.

[ndgrigorian]

there are also kernels in extensions which will have to be ignored

[antonwolfy]

I'll do that in the follow up PR, because they have to be separated to dedicated headers first. Otherwise it's impossible to ignore.