[log] target filter doc string example doesn't actually work

[Legend-Master]

This filter will not work

|metadata| metadata.target() == WEBVIEW_TARGET

https://github.com/tauri-apps/plugins-workspace/blob/753c7be0a6a78121d2e88ea0efc3040580c885b4/plugins/log/src/lib.rs#L362-L373

This overrides the target to be webview:unknown or something else from location parameter instead of WEBVIEW_TARGET

https://github.com/tauri-apps/plugins-workspace/blob/753c7be0a6a78121d2e88ea0efc3040580c885b4/plugins/log/src/lib.rs#L233