Pin libc to 0.2.189 to fix iOS build

[nicoburns]

Summary

The iOS CI job (cargo build --all --target aarch64-apple-ios) has been failing since the cargo update in faaabce, which bumped libc from 0.2.189 to 0.2.190. libc 0.2.190 makes mach_task_self available on macOS only, so num_threads 0.1.7 no longer compiles for iOS:

error[E0425]: cannot find function `mach_task_self` in crate `libc`
  --> num_threads-0.1.7/src/apple.rs:34:31

How num_threads gets into the build: boa_engine 0.22.0 → time 0.3.55 with the local-offset feature → num_threads 0.1.7 → libc::mach_task_self.

This PR runs cargo update -p libc --precise 0.2.189, which changes only Cargo.lock. The pin can be removed once a libc release includes rust-lang/libc#5612 (tracking issue: rust-lang/libc#5601).

Link to Devin session: https://dioxus.staging.devinenterprise.com/sessions/2379b63e2c5545dbb8893577abc0b00e
Open in Devin Desktop: https://dioxus.staging.devinenterprise.com/desktop/session/2379b63e2c5545dbb8893577abc0b00e?variant=devin-insiders
Requested by: @nicoburns

[staging-devin-ai-integration]

I'll fix CI failures and address comments from users with write access that start with 'Devin'.

• Disable automatic comment, CI, and merge conflict monitoring