Why doesn't Swift 6 detect as a data race?

DataRace.swift

import Foundation

class MutableState {
    var value: Int
    
    init(value: Int) {
        self.value = value
    }
}

actor MutableStateGuardian {
    private let state: MutableState
    
    init() {
        self.state = MutableState(value: 0)
        Task {
            await increment()
        }
    }
    
    func increment() {
        for _ in (1...100_000) {
            state.value += 1
        }
    }
    
    func stealState(thief: StateThief) {
        thief.state = state
    }
}

class StateThief {
    var state: MutableState?
}

let mutableStateGuardian = MutableStateGuardian()

@MainActor // <- without @MainActor annotation, data race is detected
func testCircumvention() async -> Int {
    let thief = StateThief()
    Task {
        await mutableStateGuardian.stealState(thief: thief)
    }
    while thief.state == nil {
        try? await Task.sleep(nanoseconds: 1)
    }
    for _ in (1...100_000) {
        thief.state!.value -= 1
    }
    return thief.state!.value
}