Tweak $count range check of array_fill()

We fix the `UNEXPECTED(EXPECTED(…))`, which does not make sense, and
replace the magic number with the respective macro. We also add a
test

Tweak $count range check of array_fill()

We fix the `UNEXPECTED(EXPECTED(…))`, which does not make sense, and
replace the magic number with the respective macro. We also add a
test case to verify the expected behavior for an `array_fill()` edge
case.

Closes GH-8804.

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