fix: allow running ya.sync in a sync plugin call

[dedukun]

This fixes a issue (yazi would panic) I encountered when calling an async plugin that uses ya.sync synchronously, which happened because I was creating a setup function for a plugin.

[sxyazi]

Thanks! Looks good to me.

[dedukun]

@sxyazi I think it's best to revert this change, I though that I had tested this but it seems that this solution is not working as expected.

When trying to add a bookmark with https://github.com/dedukun/bookmarks.yazi the plugin panics with the error

  2024-02-20T22:50:43.706643Z ERROR yazi::lives::lives: error converting Lua nil to function
    at yazi-fm/src/lives/lives.rs:66

For some reason the if condition with ya.SYNC_ON is met when using the ya.sync method in entry asynchronously (even though it works correctly if the method exists but is not called, which makes it seem that it is loaded correctly).

[sxyazi]

Okay, I'll fix it in the next PR.