Rename account causes `IllegalThreadStateException`

[rfc2822]

1. Create an account.
2. Rename the account.
3. Watch adb logs:

 E  Couldn't rename account
java.lang.IllegalThreadStateException: AccountSettings may not be used on main thread
	at at.bitfire.davdroid.settings.AccountSettings.<init>(AccountSettings.kt:67)
	at at.bitfire.davdroid.DaggerApp_HiltComponents_SingletonC$SingletonCImpl$SwitchingProvider$1.create(DaggerApp_HiltComponents_SingletonC.java:1881)
	at at.bitfire.davdroid.settings.AccountSettings$Factory.create$default(AccountSettings.kt:61)
	at at.bitfire.davdroid.sync.AutomaticSyncManager.enableAutomaticSync(AutomaticSyncManager.kt:66)
	at at.bitfire.davdroid.sync.AutomaticSyncManager.updateAutomaticSync(AutomaticSyncManager.kt:145)
	at at.bitfire.davdroid.sync.AutomaticSyncManager.updateAutomaticSync(AutomaticSyncManager.kt:118)
	at at.bitfire.davdroid.repository.AccountRepository.rename(AccountRepository.kt:241)
	at at.bitfire.davdroid.repository.AccountRepository$rename$1.invokeSuspend(Unknown Source:15)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:100)
	at android.os.Handler.handleCallback(Handler.java:995)
	at android.os.Handler.dispatchMessage(Handler.java:103)
	at android.os.Looper.loopOnce(Looper.java:248)
	at android.os.Looper.loop(Looper.java:338)
	at android.app.ActivityThread.main(ActivityThread.java:9067)
	at java.lang.reflect.Method.invoke(Native Method)
	at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:593)
	at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:932)

We also need better tests because account renaming is broken too often.