clippy: fix manual_ilog2 lint #6040

Job	Run time
L10n/Clap Error Localization Test	1m 45s
L10n/French Integration Test	1m 42s
L10n/Fluent Syntax Check	17s
L10n/Installation Test (Make & Cargo) (macos-latest, feat_os_macos)	7m 5s
L10n/Embedded Locale Regression Test	1m 40s
L10n/Locale Embedding - Cat Utility	46s
L10n/Multi-call Binary Install Test (macos-latest, feat_os_macos)	4m 52s
L10n/Installation Test (Make & Cargo) (ubuntu-latest, feat_os_unix)	8m 8s
L10n/Locale Embedding - Multicall Binary	2m 52s
L10n/Multi-call Binary Install Test (ubuntu-latest, feat_os_unix)	4m 7s
L10n/Build and Test (windows-latest, feat_os_windows)	8m 34s
L10n/Locale Embedding - Ls Utility	1m 11s
L10n/Build and Test (macos-latest, feat_os_macos)	4m 41s
L10n/Locale Embedding - Cargo Install	1m 3s
L10n/Build and Test (ubuntu-latest, feat_os_unix)	4m 50s
L10n/Locale Support Verification	8m 37s
L10n/Locale Embedding Regression Test	2s
	1h 2m 12s

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