Fix clippy warning on macOS

[bayandin]

Problem

On macOS:

error: unused variable: `disable_lfc_resizing`
   --> compute_tools/src/bin/compute_ctl.rs:431:9
    |
431 |         disable_lfc_resizing,
    |         ^^^^^^^^^^^^^^^^^^^^ help: try ignoring the field: `disable_lfc_resizing: _`
    |
    = note: `-D unused-variables` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(unused_variables)]`

Summary of changes

• Initialise disable_lfc_resizing only on Linux (because it's used on Linux only in further bloc)

[github-actions]

7227 tests run: 6874 passed, 0 failed, 353 skipped (full report)

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Flaky tests (1)

Postgres 17

• test_lsn_lease_size[False]: release-arm64

Code coverage* (full report)

• functions: 31.2% (8410 of 26948 functions)
• lines: 48.0% (66769 of 139205 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
40febd7 at 2025-01-04T22:51:36.671Z :recycle:}