fix tests about comparing Arc<dyn KernelObject>

[xxchan]

These sometimes fail on my computer.
Comparing fat pointers to trait objects seems to be unstable.
ref: rust-lang/rust#46139 rust-lang/rust#69757

[coveralls]

Pull Request Test Coverage Report for Build 240640358

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 6 of 6 (100.0%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.01%) to 49.012%

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Files with Coverage Reduction	New Missed Lines	%
linux-object/src/fs/pipe.rs	1	89.74%
linux-object/src/fs/file.rs	2	62.77%

Totals
Change from base Build 239040782:	-0.01%
Covered Lines:	7418
Relevant Lines:	15135

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💛 - Coveralls

[wangrunji0408]

Oh. These tests also failed on my macOS.