fix(virtual_file): compile warnings on macos

[skyzh]

Problem

starting at commit dbb0c96, macOS reports warning for a few functions in the virtual file module.

Summary of changes

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2820 tests run: 2698 passed, 1 failed, 121 skipped (full report)

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Failures on Postgres 15

• test_sharding_split_failures[failure10]: release

# Run all failed tests locally:
scripts/pytest -vv -n $(nproc) -k "test_sharding_split_failures[release-pg15-failure10]"

Code coverage* (full report)

• functions: 28.3% (6547 of 23143 functions)
• lines: 47.0% (46235 of 98460 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
fa16e98 at 2024-04-26T19:22:04.983Z :recycle:}